With 2:2′-dipyridyl as reagent for reducible and total iron, determinations were made on samples from the western English Channel at midwinter 1946–47, at the time of the maximum of phosphate, and also in July 1936.

The midwinter results have been treated statistically and the errors of analysis assessed.

Unlike phosphate and nitrate, much of the inorganic iron occurs as particles of fair size, distributed at random in the water. In winter there is no statistically significant difference between the total iron content of samples drawn from 0·5,5,25 and 50 m. depth, the grand mean and standard deviation for the whole area being 0·25 ± o·11 mg.-atom/m.3. The reducible iron for the same depth range and area was 0·19 ± 0·14 mg.-atom/m.3. There appears to be about 0·06mg.-atom/m.3 of iron which is reasonably highly dispersed and not determinable until the water has been oxidized with bromine.

In the bottom layers of water, although the reducible fraction differs little from the overlying layers, the total iron shows a very much greater mean value and variance.

The very low content of total and reducible iron and of particulate ferric phosphate in bottom water at a position 49° 30′ N., 5° 00′ W. has been provisionally attributed to removal by a dense bed of suspension feeders, possibly the mollusc Pinna.

By a statistical examination of the analytical results it has been deduced that the particulate fraction in the upper 50 m. was distributed on an average amongst about 45 particles per litre, each containing about 0·24μg. Fe and with a diameter of about 160μ. This result has been compared with data on the distribution of iron in plankton organisms.

As a statistical average waters richer in phosphate were also richer in total iron, the atomic ratio Fe/P being about 0·57.

In July 1936 the ‘elegans’ water to the westward was much richer in both phosphate and total iron than the more eastern mixed water containing Sagitta setosa. The results agree well with the conclusions drawn from the cruises at midwinter 1946–47.

In 1933–34 concentration of iron was frequently observed in the surface layers; in 1946–47 it was not. In the earlier work the surface film was always cut and included in the sample, in the later it was not. The probable amount of a surface unimicellar film of electropositive unprotected ferric hydroxide has been calculated and agrees well with observation.

Particulate ferric phosphate was found to the extent of about 0·06 mg.- mols/m.3 This appears to increase towards the bottom.

The success of the work at Newlyn in January 1947 owes much to the willing co-operation of Capt. Creese and the crew of R.V. Sabella under very adverse weather conditions. To Mr P. G. Corbin grateful thanks are due for undertaking single-handed the supervision of all the scientific work at sea on stations never more than two hours apart for two or three days on end. The statistical development would not have been possible without the unstinted assistance of Mr G. M. Spooner.

The work of which an account is here given was largely carried out from the autumn of 1937 to the spring of 1940, when it was interrupted by the war. In taking it up again (in July 1945) while, facilities for field work are still limited, the author feels it useful to publish results as they stand and indicate where further work is considered advisable.

In examinations of the free-swimming bottom fauna of the Tamar and other estuaries, attention was inevitably drawn to the populations of Gammarus species, which make up the greater bulk of it. Before quantitative observations were planned, some interesting points came to light with regard to the qualitative composition of populations. This aspect lent itself more readily to study and, though byno means a new field for exploration, soon proved worth examining ingreater detail than previous workers had attempted.

The broad fact of a replacement of one Gammarus species by another in passing up an estuary was well enough known, though exact knowledge for the British Isles only starts from the time when G. zaddachi Sexton was recognized as a regular member of the upper estuarine fauna of the Tay (Bassindale, 1933; Alexander, Southgate & Bassindale, 1935) and of the Deben (Serventy, 1935). This species proved to be the main brackish-water species overlapping with the marine G. locusta (L.) near the seaward end, and with the fresh-water G. pulex (L.) at the river end (or ‘head’) of the estuary. The status in estuaries of two other brackish-water species, G. duebeni Lillj. and G. chevreuxi Sexton, remained obscure.

In the English Channel and Celtic Sea mackerel spend the winter months on the sea floor densely packed in places where its level is interrupted by banks and gulleys.

In the early spring the fish rise to the surface and migrate to a common spawning ground that lies far out to the westward of the Scilly Islands in the vicinity of the 100-fathom contour.

The very localized positions in which mackerel spend the winter are widely distributed throughout the area in both deep and shallow water. Large schools of migrating fish converge upon the spawning ground from many directions, therefore, in the spring for spawning.

Fish that have wintered near the land must migrate offshore to reach the spawning ground; those that spend the winter on the bottom to seaward of the spawning ground must migrate shorewards to reach it. Off the south-west of England there is no single shoreward migration to spawn in shallow water as has previously been thought.

In the North Sea the chief spawning grounds of the mackerel are also near the 100-fathom contour which, in that region, happens to lie very close to the land in the Skagerrak and along the Norwegian coast. The chief spawning migration of the North Sea mackerel is therefore towards the coast from offshore localities.

This migration is, at the same time, chiefly from shallow to deeper water.

Existing information concerning the mackerel populations on the westernside of the North Atlantic points to the probability that their spawning habits and migratory movements do not differ greatly from those of the mackerel in North European waters.

A theoretical study of the behaviour of ferric phosphate in sea water has been made with existing data. The conditions least favourable for the continued existence of ferric phosphate should occur in the upper layers of the sea during active plant growth. The formation and stability of ferric phosphate is likely to be most favoured under the more acid conditions found in the gut of many animals. Ferric phosphate is likely to be introduced into sea water in animal faeces. Experimental confirmation of this deduction is essential.

In all experimental work involving ferric phosphate in sea water, the need is indicated for very accurate control of hydroxyl-ion activity and probably pressure, and for attention to the time factor and to the physical condition of the precipitated phase. The topic is of geochemical as well as of biological interest.

Dipyridyl is a reagent for ferrous iron. Reasons are set out why in sea and lake water at high dilutions it may also determine ferric iron without presence of an added reducing agent.

Evidence is presented that ferrifluoride plays no part in the iron cycle in he sea.

Fertilizations of Ophelia bicornis Savigny were made and the larvae reared. This is the first time the larval development of any member of the family Opheliidae has been described.

The trochosphere is small and somewhat yolky; it has a broad prototroch, a narrow telotroch, a strong apical tuft and a long anal cilium.

Annulation is accompanied by the appearance of parapodial lobes and bristles. When the first pair of bristles of the third setiger protrude the larva is ready to metamorphose. It has two, sometimes three eyes.

The larva in its later stages can adhere strongly to solid objects, such as sand grains, by a secretion from the four anal papillae and the parapodial lobes. This is interpreted as an adaptive aid to settlement on sand banks swept by strong currents.

At metamorphosis the larval external cilia are lost and the bristles rapidly elongate, especially those of the third setiger.

Some of the larval bristles are slightly winged. So far only capillary bristles have been known in the Opheliidae.

It is pointed out that a development such as that of Ophelia is more typical of polychaetes as a whole than are the developments of certain species commonly used as text-book types.

1039 flounders were marked with numbered vulcanite disks in the estuaries of the Tamar and Lynher.

148 flounders were recaptured and of these seven fish were recovered a second time after one recovery and release, and one fish was recaptured on three occasions after two previous recoveries and releases.

Only two fish were recovered at a distance from Plymouth. Both had moved eastward, up the English Channel.

There was little or no growth in the winter months.

Individual growth rates were found to vary greatly.

The flounders living in the last reach of the Tamar near Saltash tended to remain in one limited area during the winter months, save for a drift down-stream of some of the larger fish. In the spring there was an upstream movement of the smaller, immature fish.

Flounders which had gone down to the sea to spawn might return to the river in which they were marked, or to the other river of the two which join to form the Hamoaze, or they might move right away from the area where they were marked.

The hypothesis is proposed that inorganic ammonia may be adsorbed on particulate matter in the sea. The random distribution of such particulate ammonia would account for the frequent ‘contamination’ reported in ammonia analyses and for the finding of nitrifying bacteria associated only with particulate matter, but never with sea water itself.

The distributions of mackerel eggs and young stages, pilchard eggs, the siphonophore Muggiaea atlantica and the chaetognaths Sagitta elegans, S. setosa, S. serratodentata and 5. lyra in the Celtic Sea in March 1939, April, May-June 1937, 1938 and 1939 and July 1937 and 1938 are described, together with notes on the hydrological conditions in April 1937, 1938 and 1939, May-June 1939 and July 1938.

Mackerel spawning started in mid-March, rapidly reached a maximum in mid-April, declined gradually through May and June and was very slight at the end of July.

The changes in intensity of spawning are accompanied by a continuous shift eastward and slightly northward of the locus of spawning. In March spawning occurred in a small area at the western edge of the Continental Shelf only. In mid-April it was spread over the greater part of the Celtic Sea, with the main activity concentrated in two centres—to the south of Ireland and to the west of the mouth of the English Channel. By May-June it had shifted farther to the east and occupied the central area of the Celtic Sea. In July there was no spawning to the westward of the Scilly Isles.

The spawning area of the mackerel appears to be confined to the shallow waters over the Continental Shelf.

No mackerel young stages were found in March. Small numbers occurred in April (maximum 174). They were abundant in May-June (maximum 8239), and very scarce in July (maximum 20).

The distribution of young stages closely follows the movement of spawning during the season.

The breeding season of the lugworms of the Whitstable area is a sharply defined one, extending for 14 days between the new moon and full moon spring tides in the second half of October. Spawning begins slowly and reaches a maximum at the intervening neap tides and then declines in intensity.

Both eggs and sperms are discharged from the burrows at extreme low water to lie on the surface of the sand. Here fertilization occurs.

No germ cells were detected in the body cavity from November to June, but from August onwards to the end of October 98% of the adult worms are ripe.

At the end of the spawning period about 40% of the adults die.

A brief description of gametogenesis and of the mature gametes is given.

Germ cells are discharged through the nephridia.

The Lernaeopodidae are a highly specialized group of parasitic Copepoda presumably derived from a Caligoid stem, and some clue to their systematic position should be found in their development. Some stages are known in ten genera, but it is only in Achtheres, Salmincola, and Clavella that the whole, or nearly the whole, series of stages has been described. There is a very strong tendencyto suppress the nauplius as a free stage though, when so suppressed, there may be moults corresponding to nauplius and metanauplius (Zandt, 1935). In some species there is certainly a free nauplius, but it probably moults into the copepodid in a very short time.

Landings of the spurdog, Squalus acanthias, at Mevagissey reflect the changes in phosphate at the neighbouring International Hydrographic Station Ei.

It is suggested that commercial landings of rays and skates ought to follow major changes in nutrient content of the overlying water with a time lag of some years. Fishery statistics for English Channel ports support this view. The dependence of the bottom in-fauna upon the fertility of the overlying water is also discussed.

Proposals to improve commercial fisheries by artificially fertilizing considerable areas of the open sea are critically examined. Such artificial enrichment is considered to be grossly uneconomic unless fishing becomes pisciculture in which weeding of unwanted algae and control of unwanted pests—competing predators and parasites—is undertaken.

It is suggested that the genera Apomatus and Protula should be revised to reflect the close similarity between P. tubularia and the two species of Apomatus, and the dissimilarity of Protula intestinum. It is further suggested that the presence or absence of an operculum is not a sufficiently important character for distinguishing Apomatus from Protula, or Filograna from Salmanica; and therefore that these two pairs of genera should be fused into two genera.

I should like to place on record the circumstances under which I saw for the first time that the male cells of the Dictyota family were not non-motile spermatia but ciliated motile antherozoids.

Spisula subtruncata is a shallow-burrowing member of the Mactridae which inhabits silty sand. Adaptations to such conditions include long frontal cilia on the gills (Atkins), and the presence of a siphonal membrane with associated mantle folds over-arching a waste canal, as postulated by Kellogg for allied species.

The mantle edges are free ventrally, but are normally closely applied except for a short distance at the base of the inhalant siphon, an effective fourth pallial aperture being so formed. Through this opening material from the waste canal is ejected.

Lutraria lutraria is a deep-burrowing species belonging to the same family. The general resemblance to Mya arenaria is due to convergence. Cleansing currents resemble those of Spisula subtruncata and there is a similar waste canal, but the siphonal membrane and the long frontal cilia associated with a silty environment are absent.

A simple photoelectric meter is described which allows the molybdenum blue formed in sea water, due to the presence of phosphate, to be estimated within that due to ± 0·25 mg. phosphate-P per m.3.

The effects of concentration of acid, molybdate, reductant, temperature and suspended particles on the rate of formation, fading and amount of molybdenum blue, formed in sea waters containing phosphate are detailed.

Intramolecular changes taking place during storage of molybdate solutions, and while being mixed with acidified sea water, have been investigated.

The hydrolysis of organic phosphorus compounds in acidified sea water at 140° C , and the prevention of arsenate formation, are described.

Procedures, resulting from these investigations, for the estimation of phosphate, and of total phosphorus, are described.

The growth of bacteria and the physical adsorption of organic phosphorus compounds in solution on the walls of glass vessels used for storage of sea water have been investigated, and a method of prevention evolved.

The external features of Skeneopsis planorbis (Fabricius) are described and compared with those of Omalogyra atomus (Philippi), Rissoella diaphana (Alder) and R. opalina (Jeffreys).

The foot has a large posterior mucous gland (Figs. 1 and 4, Pm; PI. IV, figs. 1 and 2, Al, Pl), its secretion forming a thread on which the mollusc can climb from one level to another.

Correlated with their small size are modifications of the pallial organs. Skeneopsis, the largest and least specialized, has a bipectinate osphradium, but the gill is reduced to nine filaments; the anus lies well within the mantle cavity. In the other genera osphradium and ctenidium are lost, though the latter may be represented in Rissoella by a small tract of ciliated epithelium. In the absence of a ctenidium the animals depend entirely upon pallial respiration and the stream of water through the mantle cavity is maintained by other means: from the anus strips of ciliated epithelium pass forward to the mouth of the mantle cavity, causing a strong exhalant stream and carrying away the faecal pellets. There is a compensating inhalant flow. The kidney (PI. IV, figs. 1 and 2, K), with its rich vascular supply, has migrated into the tissues of the mantle, increasing its respiratory efficiency.

The occurrence in the summer of 1945 of a swarm of Physalia physalis L. off the south-west coast of the British Isles has initiated a survey into records of its appearance on the Atlantic coasts of Europe during the past 100 years. Unpublished records for 1912, 1913, 1934 and 1935 were discovered and are listed with those already known. The 1945 strandings are considered in detail in conjunction with meteorological data for the period involved. It is concluded that winds, rather than water movements, are the main factor in transporting the swarms towards the British Isles and it is considered likely that the swarms come from the Azores-mid-Atlantic region rather than from the Canaries-Gibraltar district.

Associated with the Physalia were Lepas fascicularis and L. pectinata, some Velella, a few turtles (Caretta caretta), and possibly an Opah fish (Lampris luna), all of them, with some reservation respecting the last-named, surface organisms that would come under the same meteorological influences as the Physalia.

A living specimen of Physalia gave an opportunity to observe the method of feeding of which few previous first-hand accounts exist. The capture of the prey by the dactylozooids and its subsequent digestion by the gastrozooids is illustrated by photographs from life and is described in some detail. It is suggested that the rolling of the pneumatophore from side to side, dipping the crest in the water, is a calm-weather habit directed to keeping moist the upper surface exposed to the air.

Loch Craiglin cannot be considered as merely an isolated basin of Loch Sween. Its shallowness, the great growth of vegetation round the shore and the fluctuations in salinity make it atypical. On the more complete isolation of the loch with the making of the dam, these conditions led to a lack of circulation, a consequent development of hydrogen sulphide in the deep water and very high pH values near the surface. One could not therefore expect the plankton to be very similar to that in the outside loch (see, however, Marshall, 1947). Unfortunately there are no records of seasonal variation before fertilization was begun. In spite of these drawbacks Loch Craiglin was a convenient and manageable area for small-scale experiments on fertilization.

The experiments may be divided into two groups, those which were not followed up in detail and those in which the plankton and hydrographic results were followed from day to day. The former, made during the earlier stages of the work, are mainly described in the previous papers and led to the conclusion that the richness in phytoplankton of Loch Craiglin in 1943 was probably caused to a large extent by fertilization. Those of the second group, described above, were made to test special points and different fertilizers. Two experiments made during the summer of 1944 had apparently no effect on the phytoplankton but a third in which a very large excess of fertilizer (ten times the normal quantity) was added, gave a good increase after an initial lag. At that time the attached algae were abundant and their needs apparently had to be satisfied before any nutrients could be used by the phytoplankton.

The remaining experiments, which were therefore made during the winter, showed that commercial ammonium sulphate, ammonium nitrate and monoammonium phosphate could replace the sodium nitrate and superphosphate used hitherto. Two further experiments in the following spring using ammonium chloride and urea did not, however, prove effective. All the salts used had been found in laboratory tests by Miss F. A. Stanbury to be suitable for diatom growth, and the reason for the failure of these two in the loch is unknown.

The utilization of the nutrients was extremely rapid even in winter but it is probable that their disappearance is not entirely caused by the phytoplankton or bottom-living algae but partly by adsorption on the bottom mud or by suspended matter. On one occasion it may have been caused by a serious fall in loch level.

The zooplankton which during the first year of fertilizations was richer in Loch Craiglin than in the outside loch diminished in the second year and remained poor thereafter in spite of, or perhaps because of, the intensive fertilizations. The dense phytoplankton and other vegetation raised the pH at times to levels dangerous to animal life.

Stolonica socialis (Hartmeyer) and Distomus variolosus Gaertner are two species of styelid ascidians with a capacity for budding and colony formation, found on both sides of the western end of the English Channel. Distomusoccurs immediately below the level of extreme low spring tides, commonly encrusting the sides of rocks and laminarian bases. Stolonica is more usually found by dredging in deeper water, on the upper sides of stones or gravel bottom. Their external appearance and general internal anatomy have been well described and beautifully illustrated in the monograph of Lacaze-Duthiers and Delage (1892), while the process of budding has been investigated by Selys-Longchamps (1917).

The work includes an investigation of the intertidal distribution of several species previously studied in Cardigan Bay. Twelve localities in the neighbourhood of Plymouth were selected for study, showing a range from conditions of extreme exposure to surf action to conditions of maximum shelter. The main features of rock configuration and surf action at the different localities are briefly described.

The method of investigation is described, and results obtained for the zonation of the fucoids on Church Reef are compared with the results of Colman (1933). It concluded that the method of survey adopted in the present work yields results of a high degree of accuracy.

The horizontal and vertical distributions of the flora are described and related to the intensity of surf action. This is followed by a discussion of the effects of wave intensity and wave frequency on the distribution of algae in general. The importance of the frequency of wave shock in the mid-tidal region of the shore, and its influence on algal colonization, is stressed. An attempt is made to arrange the algae studied in order of decreasing tolerance of surf.

The distribution of the selected species of animals at the different localities is described; and a discussion follows on the effect of wave action as a presence or absence factor in horizontal distribution, and as a modifying factor on vertical zonation. The effect of surf on the size of individuals of certain species is also commented upon.

The relation of the plant and animal species to different percentage exposures to the air at different shore levels is discussed.