A bio-assay of the nitrogen which was available to two phytoplankton species with their associated bacteria in an off-shore water is described.

The concentrations found by assay (11·5 and 13μg N/1.) were similar to the concentration of total inorganic nitrogen compounds found by analysis (10μg N/1.).

Of the organic nitrogen normally present in solution in sea water, an insignificant quantity appears to be available to the plant-bacteria community.

Idotea metallica Bosc occurs occasionally in plankton from waters off the west coast of Britain, but since it does not seem to be a British resident it was excluded from a recent review of the genus Idotea (Naylor, 1955 a). Accounts of the distribution of /. metallica seldom distinguish between occasional records and resident breeding localities, and this note attempts to explain its occasional occurrence in Britain.

Microdiffusion using a Cavett flask has been employed instead of vacuum distillation for the separation of ammonia from sea water; diffusion is approximately 75% complete after 24 h at 70°C. The recovered ammonia is determined by a modification of the phenate-hypochlorite method.

Raney nickel in the presence of ethylenediamine-tetraacetic acid has been used for the reduction of nitrate and nitrite to ammonia. The latter is separated by microdiffusion and determined colorimetrically. The method showed a coefficient of variation of 2·5% on a sample of sea water containing

No interference was encountered from a variety of organic nitrogen compounds.

In the 4th to 8th thoracic segments of decapod Crustacea, at the bases of the peraeopods, sensory organs of various kinds have been found. They have been observed in Homarus vulgaris, Astacus astacus, Palinurus vulgaris, Eupagurusbemhardus, Carcinus maenas, Maia squinadoand described in greater detail for Homarus, Carcinus and Maia.

In all species examined there is in each peraeopod a proprioceptor consisting of a thin muscle with various nerve elements which extends from a point of the endophragmal skeleton situated near the ventral ganglia to the anteroventral part of the coxa. In the 4th to 7th thoracic segments of Homarus, in the 4th to 8th of Palinurus and Astacus, and in the 4th of the Brachyura, the receptor muscle is proximally attached to the tip of a chitinous projection of the endophragmal skeleton for which the term ‘receptor rod’ is proposed. In other instances it originates on the plate of the endosternite.

The nerve components of this ‘muscular receptor’ are of two sorts: (1) motor nerves spreading their branches over the whole length of the muscle, and (2) processes of the sensory neurons distributing their ramifications on the connective tissue associated with the muscle at its proximal end. The arrangement of the sensory elements is different in various species, but they all exhibit one feature, unusual in invertebrates, viz. their cell-bodies are situated within the central nervous system and not outside it.

Details are given of the breeding biology, including the fecundity, of the Long Rough Dab deduced from samples taken in the Clyde Sea area from October 1953 to April 1955. Where possible breeding is related to the condition of the fish; the index of condition is based on the length-weight relation.

The weight of Long Rough Dabs of each sex and stage in maturity increases as a power, slightly greater than the cube, of the length. An annual cycle of fluctuations of this power is seen in the immature females, and indicates how changes in condition at different seasons affect the different size-groups. The measure of condition is taken as the expected weight of a 20 cm Long Rough Dab, and the changes in this weight are followed through the sampling period for males and for immature, maturing and spent females. All groups tend to be in best condition during November and December followed by a decline to the spawning time, in March and April, after which there is a slow recovery.

Methods of extraction of the toxin from cultures of Gymnodinium veneficum are described. This is now done by dialysis and evaporation under reduced pressure. The toxin molecule must be large, as it cannot penetrate a dialysis membrane; it is soluble in water and the lower alcohols, but insoluble in ether and chloroform. It is unstable in acids, turning into another toxic product, and is decomposed by hot alkali, though in neutral solution is more or less thermostable. The toxin as it occurs in sea water is not the same as paralytic shellfish poison, but there are some resemblances between this and the 'acid extract', though much more work is needed to check this point.

The action of the toxin on a variety of animals is described, and an attempt is made to devise an approximate assay technique using gobies as the test animals.

The action has also been observed on a range of isolated preparations, and although the final conclusion as to the mode of action is not quite clear, we feel confident that the site of action in whole animals is in the nervous system, probably acting on ganglion transmission. With regard to the mode of action it depolarizes nerve and muscle membranes. It also abolishes the potential across frog skin without measurably altering the skin resistance.

This depolarization probably occurs by interference with the sodium exchange mechanism, allowing rapid entry of sodium into the cells.

The spectral composition of the light of Chaetopterus variopedatus has been measured by means of spectral niters and multiplier phototube. Spectral emission extends from about 405 to 605 mμ, with a maximum at about 465 mμ. The spectral curve of Chaetopterus light is compared with a human visibility curve (scotopic vision), a visibility curve for Limulus, and an absorption curve for fish visual purple. Luminous efficiencies, based on these curves, are calculated.

The variation in the fecundity of a fish species from year to year has not received much attention, although the changes in the numbers of young fish in the plankton are well documented for the Plymouth area (Russell 1930–47; Corbin, 1948–51). The most important work considering fecundity fluctuations is that of Simpson (1951) who, working onPlaice, Pleuronectes platessa L., concluded that during 1947,1948 and 1949 there was a steady decrease in the number of eggs laid, this being due to a decrease in the mean size of the spawning fish which he showed to be correlated with the egg numbers. Simpson's interest in the fecundity was to provide a more accurate estimate for determining the number of plaice in the total population from planktonic egg surveys similar to the work of Buchanan-Wollaston (1923). He did not consider in detail whether the fecundity for a given length might change from year to year. It is this problem which will be considered here. Estimates of fecundity of Long Rough Dabs, Hippoglossoides platessoides (Fabr.), will be analysed, and Simpson's Plaice data will also be considered.

Cell ovoid to almost sphaeroidal in face view of right or left valve, lenticular to almost sphaeroidal in view showing junction of valves, in both views flagellar pole flattened, length (10) 14–17 (22), breadth (9) 11–15 (20), thickness (5) 6–8 (18) μ. Two valves of cellulose, each with a striated band at margin, band wider in larger cells, striations about 0–5 μ apart, remainder of valve surface with poroids, apparently in rows, 0–25μ apart, poroids 0.2–0.2 μ. diameter; right valve with shallow indentation, about 2 μ wide, at flagellar pole, usually lying to left of centre line; left valve with small projecting flange, about 2 μ wide, bearing flagellar pores and fitting into and over indentation on right valve; the two flagellar pores of unequal size, in apical view larger nearly triangular, smaller circular, in left valve view smaller pore to left of larger.

A study has been made of the ecology of the small intertidal lamellibranch Lasaea rubra at various tidal levels at Plymouth and Wembury. In addition, experiments have been carried out to investigate physiological and behavioural differences arising from varying amounts of submersion at different tidal levels, and the following findings have been made.

During the first hour after their submersion by sea water, L. rubra from high up the shore filter at a rate approximately twice that of animals which live lower down. After 2 h, however, both sets of animals filter at the same rate.

High-level animals respond significantly faster to wetting by splash and can tolerate a considerable range of salinity. They also respire at a rate approximately twice that of low-level animals. Respiration, however, is not detectable when the animal is not immersed in sea water.

Measurements were made on the intact retinae dissected from freshly caught deep-sea fish. The unbleached retinae of such fish are not rose-pink like the retinae of most coastal fish or purple like the retinae of most freshwater fish, but are golden in colour.

The golden colours are of photosensitive pigments which give retinal absorption curves similar in shape to frog's rhodopsin, but with maxima of absorption displaced on the average about 15 mμ. towards the blue end of the spectrum. The names ‘chrysopsins’ or visual golds are suggested for this group of pigments.

The density of such photosensitive pigments is often very high. Retinal density changes on bleaching of more than 1.0 has been found for several deepsea fish. These probably correspond to absolute retinal densities of pigment of about 1.3, i.e. the absorption of 95% of blue-green light striking the retina.

The conger and silver freshwater eels have retinae containing similar golden-coloured pigments. These eels begin their lives in the deep ocean and return there when mature to spawn.

The significance of this type of photosensitive pigment in the vision of deep-sea fish is discussed, and an estimate is made of the depths at which deepsea fish will see daylight.

The taxonomic status and nomenclature of the hermaphrodite forms of Fucus (other than the alga currently known as F. spiralis L. and certain hybrid forms) usually included under the name Fucus inflatus L. by European authors, but under several specific names by N. American and some other authors, is discussed. It is considered that the numerous forms described are best interpreted for the present as forms of a single, extremely plastic and widely distributed species.

The distribution and ecology of subspp. anceps and edentatus of F. distichus L. emend. Powell (1957) in Britain and Ireland is described in detail, based on recent ecological surveys and critical examination of all past records.

F. distichus anceps is a small form confined to certain very exposed coasts in the north and west of Scotland and Ireland, where it reaches the southern limit of its geographical range. This plant may be a relict form in Britain, existing now only under an extraordinarily narrow range of rigorous habitat conditions; it is not thought to be actively extending its range southwards at the present time. The ecology of subsp. anceps is considered principally in relation to that of other reduced fucoids found on exposed British shores, viz. F. spiralis f. nana and F. vesiculosus f. linearis; all three forms are illustrated by photographs and means of distinguishing them are described. The lifespan of subsp. ancepsis thought to be 2 to 3 years at some Irish sites, but may be longer at some of the Scottish sites.