The exhalant siphon of Xylophaga is greatly reduced and its opening is situated within the burrow. Faeces accumulate in the posterior end of the burrow in a compact mass.

The ctenidia and labial palps of Teredo, Bankia and Xylophaga are modified and reduced, unlike those of the Pholadidae. The ctenidia are flat and homorhabdic and possess no ciliary sorting mechanisms; they consist of the outer demibranch only.

The ctenidia of Xylophaga are composed of a direct lamella; those of Teredo and Bankia are divided into anterior and posterior portions connected by a branchial groove which is an extension of the marginal food groove of the gill. The number of filaments in the anterior portion of the gill varies according to the species, and is of assistance in identification.

The labial palps of Teredo norvegica are least reduced; in Xylophaga dorsalts reduction is greater, though selection of food material is still exercised. The greatest reduction has occurred in Teredo megotara and in T. navalis where there is no selection.

The ciliated mantle tracts in Teredo and in Xylophaga play an important part in limiting the quantity of food particles passed from the ctenidia to the mouth.

An account is given of the distribution, life history and trematode parasites of Littorina neritoides on the Plymouth Breakwater; a few observations from other localities are included.

The smaller snails are most abundant on the exposed southern slopes of the Breakwater. Many of the larger ones live more or less permanently in water in small cylindrical pits on the top of the Breakwater. This habitat is apparently very similar to that described by Fischer-Piette (1932) as occupied permanently by this species at Cap Martin; Lebour (1935) has sometimes found it in water in other places in the Plymouth area.

The conditions necessary for metamorphosis of the larvae, the need of the adults for shelter from the force of the waves, and the requirements for spawning appear to be of more importance in determining the choice of habitat than the negatively geotactic and varying phototactic responses found in this species by Fränkel (1927).

The breeding season lasts from September to April. The males are ripe about two months before most of the females. Experimental evidence is given which makes it most improbable that there is any downward migration for spawning. From the examination of plankton samples it appears that there is a fortnightly spawning rhythm coincident with high tides, and that even the snails living in water discharge their eggs only at these periods.

The distribution of the size groups is discussed. The proportion of males decreases significantly in the larger size groups and it is probable that there is a difference in the growth-rate of the sexes.

If the number of infections with (a) trematode parthenitae and cercariae using Littorina neritoides as first intermediate host only, and (b) encysted metacercariae using L. neritoides as second intermediate host only, are plotted against the size of the snails, two different curves result. The first shows a low rate of infection in the small size groups, but a steep upward slope rising to 91% in the large size groups. The second shows a curve increasing uniformly to 87% infection.

Possible interpretations are discussed, and it is concluded that the difference is probably due to the fact that primary infections cause accelerated growth in the host.

The faunal analysis of forty-eight samples taken with a coarse tow-net across the intertidal waters of Kames Bay during 1936 shows that the night migrant crustacean population falls into two well-marked groups: (a) those species which live in the intertidal sand and perform simple vertical migrations at night-time into the intertidal waters, and (b) those which are carried in by the tide into the intertidal area from various habitats which lie beyond the low-water mark of spring tides. In the former group the species of the genera Bathyporeia and Pontocrates are dominant and they retain their zonation as migrants, the population consisting of individuals in all stages of maturity. This is in sharp contrast to the latter group, typified by Gammarus locusta and Idotea viridis, which occur over the whole tidal range with a population in which the young immature stages are dominant. The Haustoriids Urothoë brevicornis and Haustorius arenarius occur as inhabitants of the sand, the former appearing occasionally in the tow-net samples and the latter absent from them. The Cirolanid Eurydice pulchra performs both day and night migration for the purposes of feeding.

Discussion of the results indicates the lines along which further investigations may be carried out.

Manila ropes and trawl twines, and cotton nets, have been immersed in clean sea water for periods up to 14 months, some with alternate wetting and drying, some wet all the time, but in both cases accompanied by storage in air after immersion. All the untreated specimens perished, but the 700 lb. manila ropes retained at least 40% of the original tensile strength.in every case in which a copper soap had been included in the treatment. A previous treatment with cutch is a considerable advantage as shown by the 500 lb. manila ropes and trawl twines, though cutch alone is worthless. Coal tar distillates after cutch are, however, more useful than when used alone, and their mixture with copper soaps gives excellent results. Cutch fixed with bichromate gives tolerably good preservation on nets up to 6 months, but is a poor preservative for trawl twines and ropes which are expected to have a long life. The choice of the copper soap used depends upon the material to be preserved. Naphthenate is the most soluble and penetrates thick ropes excellently; on fine nets it leaches out easily. Oleate is cheaper, but its penetration is less; it does very well with tar on twines and nets. Resinate is the least soluble, but is useful with creosote oil or tar. On account of their greasy nature naphthenate and oleate act as lubricants in ropes.

Immersion tests on other preservatives, kindly suggested by Dr S. G. Barker, are to be begun.

In a study on the possible occurrence of hydroxylamine as an intermediate compound in the oxidation of ammonium salts to nitrites in sea water (see Cooper, 1937), the method of Blom was tried in order to estimate the hydroxylamine. The method consists in the oxidation of the hydroxylamine by a solution of iodine in acetic acid, removal of the excess of iodine with N/Io thiosulphate, and estimation of the nitrite so produced by the Griess method; the method has been used by several workers for the estimation of small amounts of hydroxylamine in biological material.

The method had not been used for such small amounts of hydroxylamineas would be expected in sea water, and it was therefore tested at high dilutions. It was found that nitrite itself, however, could not be recovered after treatment with the above reagents, and it was noticed that in many cases a precipitate (probably sulphur) was produced, and a distinct smell of hydrogen sulphide was often apparent. It was thought probable therefore that the loss was due to the interaction of the nitrite or the red dye with the thiosulphate used for removing the excess of iodine. This view was confirmed by noting the removal of the red colour, the appearance of a precipitate, and the smell of hydrogen sulphide when a solution of thiosulphate was added to a solution of the dye.

Experiments were therefore set up to determine the amount of thiosulphate that could be present in excess without interfering with the estimation.

One of the lobsters kept in the tanks of the Plymouth Laboratory moulted on the night of 2 0 August 1940. This opportunity was taken to examine the changes in water content and osmotic pressure of the freshly moulted as compared with unmoulted lobsters. Though only one recently moulted individual has been examined, the results seem to be worthy of note since so far as we are aware no data are available on the subject in regard to Homarus. The biology of moulting among lobsters has received the attention of many investigators (vide Herrick (1895) and Drach (1939) for summary and literature).

The water content was determined by distilling the fresh lobster together with a known weight of sea water under xylol. This method is a modification of that of Dean and Stark which one of us (A. G. L.) has tried on a number of animals and found to give accurate results. The density was estimated by a modification of a method previously described (Lowndes, 1938). Osmotic pressure of blood and the external medium were measured by Baldes's (1934) modification of the Hill thermoelectric technique, as employed by one of us (N. K. P.) in the study of prawns and other crustaceans. The water content of the moulted skin was calculated from its dry weight taken after dehydrating in a hot air oven for 48 hr. at 105° C. Osmotic pressure was measured 17±6 hr. after moult; density and water content after 34±6hr. The temperature of sea water at which the density was estimated was 17° C.

An investigation has been made of the species of Sagitta present in parts of the Irish Sea, their relative occurrence, and the annual number of reproductive cycles of each species. Three stages of maturity as described by Russell (1932a) have been used. To determine the maturity the Sagitta were transferred to a solution of 75% alcohol and stained with borax carmine.

S. elegans Verrill and S. setosa J. Müller were collected in Liverpool Bay and in Port Erin harbour, Isle of Man. The former species was predominant at Port Erin. The coasts of Liverpool Bay have been added to the permanent range of S. setosa.

At Port Erin there appears to be but one chief spawning period for S. elegans which extends generally from January through May. Following May the young forms appear in numbers and gradually mature through December to repeat the annual cycle.

There appear to be two main breeding seasons for S. setosa in the outer Mersey Channels. The first and most noticeable begins in April and extends into June. There is evidence for a second breeding period in August.

Both species were found in the samples taken from Morecambe Bay and Anglesey. The stage of maturity of these agreed with the Sagitta caught at the same time at Port Erin and Liverpool.

The total monthly catches of Sagitta from Port Erin and the outer Mersey Channels have been recorded.

In a recent issue of this Journal Dr Hughes (1940) published records of a successful attempt to rear oysters in tanks on the River Yealm during the summer of 1939. In this paper he referred to plans for the following year, and it therefore seems desirable to record a few notes on the 1940 season.

Since Dr Hughes left Plymouth I have kept in touch with Mr J. Kingcome, the owner of the fishery, and from time to time have visited his tanks and proffered technical advice. In this I have had the willing co-operation of Mr H. A. Cole of Conway whenever his opinion has been sought. Mr King come has most readily adopted suggestions we have made, and it is to his careful attention and unremitting work that the successful results here recorded are due.

Further History of the 1939 Spat

Dr Hughes mentioned that in August 1939 some of the larger spat were detached from the tiles and placed in cages in the estuary of the river. At the time of writing (mid-October 1940) these range from 4.5 to 8 cm. in diameter. The remainder of the spat spent the winter on the tiles in tank C (Hughes, 1940, Fig. 1), being given almost daily changes of water from the estuary. They were detached from April to July 1940 and placed like the others in wire-meshed cages just above low-water mark spring tides. These oysters have by no means reached the size of those which have been out since August 1939, the size range being 2–4 cm. in diameter.

The notes collected in this paper are a continuation of earlier observations on British and Norwegian hydroids and their medusae. The observations were made at the Biological Stations of Herdla (Bergen), Millport and Plymouth.

The hydrorhiza of Myriothela cocksi is described. It bears adhesive tentacles covered by perisarc, which adhere to the substratum by their flattened extremities.

The chitin forming a disk of adhesion is thick, and is attached to the mesogloea of the tentacle. The terminal ectoderm persists.

The hydrorhiza of M. cocksi and of species such as M. capensis, M. penola, and M. phrygia, etc., is built on a common plan. In the latter species the perisarc is reduced to adhesive disks more firmly attached to the mesogloea.

The method of growth of M. cocksi is recorded.

The structure and method of attachment of the claspers of M. cocksi to the egg membrane is described. The mesogloea at the tip of the clasper fuses with the egg membrane after the disappearance of the terminal ectoderm.

Evidence is given for the view that the claspers of M. cocksi represent a specialized part of the hydrorhiza.

In October 1935, investigators from eleven countries represented on the International Council for the Exploration of the Sea met at Lowestoft to discuss the co-ordination of the results of herring research (Cons. Int. 1936 p. 7).

The foregoing pages include an account of the anatomy and histology of the male and female genital ducts of Ocenebra erinacea, Nucella lapillus, Nassarius reticulatus and Buccinum undatum. Observations have also been made on the mode of functioning of the ducts and the formation of the egg capsules.

In both male and female it is possible to divide the genital ducts into a narrow and thin-walled proximal section which leads from the gonad and opens into a thick-walled glandular distal region, and in this respect the Stenoglossa agree with the mesogastropods. Near the junction of these two portions, in the female, arises the gonopericardial duct, which puts the genital duct into communication with the pericardial cavity; in males this structure i s lost or reduced to a vestige lying in a similar position.

In males the upper part of the proximal region of the genital duct is used as a vesicula seminalis and the epithelium is capable of taking up and digesting effete or superfluous sperm. Sperms are passed from it into the anterior, distal region during the act of copulation, and secretion from the glands is mixed with them and provides the medium in which they are transferred to the female. In Ocenebra and Nucella this glandular region, the prostate, extends only as far as the opening of the mantle cavity, from which a continuation of the duct, without glandular walls, runs to the penis. The entire distal half of the male duct shows evidence of having been derived from an open seminal groove such as is found in Littorina.