Some features of the organization of the endostyle of Ciona intestinalis are described. Autoradiographs show that bound iodine is present in a limited area of the epithelium (zone 7), where it is associated with characteristic secretory inclusions which are found only in this zone. These are regarded as providing the molecular basis for the iodination process, and are termed 'thyroidal granules', since they resemble in certain properties the similarly named granules of the endostyle of the ammocoete; it is concluded that they are homologous with these and, through them, with thyroid colloid. Their existence provides evidence that the iodination process is a product of biochemical specialization, and implies that it results in the formation of an hormonal secretion. It is concluded from the distribution of bound iodine over the pharyngeal epithelium and in the food cords that this iodinated secretion is carried in the latter into the intestine. Bound iodine is also present in the cuticle of the test; it is suggested that this may differ from the situation in the endostyle in being a consequence of the iodination of a skeletal protein secretion such as is known to occur in many invertebrates. Prior immersion of the animals in thiouracil solution largely eliminates bound radio-iodine from all of the sites mentioned, although a little may sometimes be detectable in the food cords and cuticle. The results are discussed in the light of recent work on Amphioxus and the ammocoete larva, and attention is drawn to their bearing on current views on the relationship between vertebrates and protochordates.

The apparatus described in this paper was constructed for the purpose of sampling the zooplankton standing crop in the ocean in a quantitative manner.

A meter is described, which will record both the depth and amount of water which a net filters as it is hauled vertically through the water. The meter records on a smoked glass cylinder.

The meter is mounted in a brass drum which is positioned in front of the silk filtering section of the net. In front of the meter a long canvas sleeve carries the throttling rope which closes the net by the Nansen method.

Calibration of the meter for depth is done by using reversing thermometers and lowering to a series of suitable depths. Flow calibration is easily accomplished in the field by towing the canvas sleeve and meter without the silk net.

The method of smoking the glass cylinders and taking photographic records of them is described.

From the records it is possible to study the complete behaviour of the net below water—what depth range it has fished, how much clogging occurred, the depth of closure, etc

Mytilus galloprovincialis Lmk. is recorded as dominating the mussel population on the north coast of Devon and the north and south-west coasts of Cornwall from Instow to the Lizard. It was also found less frequently on the coast of South Wales from Angle to Cardiff and on the south coast of Cornwall from the Lizard to Plymouth.

The chief distinguishing features of M. galloprovincialis from Cornwall are summarized, in comparison with M. edulis L.

M. galloprovincialis is apparently intolerant of estuarine conditions, but otherwise appears to be ecologically similar to M. edulis.

M. galloprovincialis is not resistant to infection by Mytilicola intestinalis, but appears to be less affected by the parasite than is Mytilus edulis.

The synonymy of the species is briefly discussed and it is concluded that, although earlier workers tended to confuse M. ungulatus L. (recorded also as M. ungulata and M. angulata) with M. galloprovincialis Lmk., the two types are distinct. M. ungulatus is a name of doubtful validity applied by Linnaeus to a distorted form of M. edulis.

Populations of Scrobicularia plana with densities up to 1025 per m2 are found in the Gwendraeth Estuary.

In a region where the population density was about 500 per m2 it was found that some specimens lived for 16‐18 years and reached a length of 54 mm. An approximate growth curve is given.

There is very little successful settlement of spat in the sampling area; less than 2% of the shells were under 10 mm in length in July 1955. This low figure is attributed to the feeding activities of the dense adult population making the area difficult to settle in.

During 1952–54 a survey was made of the Polychaeta living in the offshore bottom deposits of the south of the Isle of Man. These deposits range from stones and coarse gravel to soft mud; samples were obtained with a van Veen grab sampler and various dredges.

It was found that, although some species were widely distributed, each bottom deposit had a typical fauna, and that where the deposits graded into one another the polychaete fauna was also mixed. The distribution of each species appears to depend mainly on its mode of life and feeding habits; some can exist in several types of deposit or habitat, while others are very much restricted in their distribution.

The Polychaeta formed a high proportion, numerically, of the macrofauna, exceeding any other animal group, except possibly in the coarse gravels. However, the density of the polychaete population was low compared with other areas of the British Isles, and this may be correlated with the comparatively low biomass in the area.

In a sample of over 1000 rays belonging to four species of Raia examined at Plymouth between May 1955 and August 1956, the ‘very rare’ monogenetic trematode Dictyocotyle coeliaca Nybelin, 1941 (total of four previous records) was found in the coelom of thirty-five out of 135 specimens of Raia naevus but absent from 478 R. clavata, 420 R. montagui and 34 R. brachyura.

Owenia may feed either by ciliary means or by swallowing sand and detritus. The gut consists of three main parts, a fore-gut or stomach which is secretory, a non-secretory mid-gut region which is absorptive, and a hind-gut which is non-secretory, non-absorptive and serves to elaborate and store the faecal pellets. The mid-gut contains coproporphyrin III and also phaeophorbide-6, to which the green colour is due. The green pigment in the epidermis is also phaeophorbide-ft, but phaeophorbide-a is apparently absent from the body.

Determinations of the concentration of fat and glycogen in the body wall, in different parts of the gut and in the coelomic cells are described in Amphitrite and Arenicola. It is suggested that the trephocyte system constitutes a store of fat and glycogen derived from a primary store in the absorptive parts of the gut itself. In Arenicola and Nereis surplus fat is removed from the gut itself through the blood or directly by amoebocytes; the fat deposited in the epidermis and the glycogen in the peritoneum. In these worms the coelomic trephocytes are solely concerned with the maturation of the gametes. No relationship can be established between these cells and the chloragocytes. In Amphitrite and Terebella fat is stored also in the coelomic trephocytes which may derive their contents directly from the gut or from the body wall. Glycogen is stored in the trephocytes in Amphitrite, and in Arenicola in the peritoneum. Thus while large amounts of fat and glycogen are found in the trephocytes in Amphitrite, the total amount present in the body is no more than in Arenicola which lacks a well-developed trephocyte system, and in this species a larger proportion of fat and glycogen is found in the body wall.

Several strains of Stichococcus bacillaris Naeg. and of the marine S. cylindricus Butcher were all found to fit morphologically in Naegeli's species. Both the marine and non-marine strains grow well in either fresh- or sea-water media. S. cylindricus must therefore be regarded as a synonym of S. bacillaris. Three marine Chlorella strains including C. ovalis Butcher and C. stigmatophora Butcher were also found to be quite unexacting about salinity. The significance of small differences, particularly of growth rate, is discussed with regard to non-sexual organisms. In general, widely based species are advocated for such organisms, with the clonal lines, where appropriate, designated by the reference number of a recognized culture collection.

Tigriopus fulvus can live normally within a salinity range of from 4·2 to 90%.

In waters of salinities above 90% it falls into a state of apparent death from which it can recover if transferred back to lower salinities.

The relation between immersion period and the recovery period is only slightly different at different salinities.

The lethal temperatures vary between 32·0 and 41·8°C depending on the salinity of the sea water, the lethal temperature being higher in higher salinities.

The fluctuations in salinity and temperature in the pools where the animals were collected are well within their tolerance limits.

T. fulvus is well adapted to its habitat.

Patella vulgata gives a positive response to splashing with sea water or water of high salinity, and a negative response to fresh water or water of low salinity. The intensity of the positive response broadly corresponds with the salinity of the water used. There is a greater response to splash and a greater tolerance to reduced salinity in limpets from high-tide than in those from low-tide regions. A positive response is given to NaCl solutions of concentrations approximately equivalent to sea water, while a supra-normal response is given to concentrations somewhat above that of sea water. The perception of salinity is by receptors in the cephalic tentacles and mantle fringe.

The chromosomes of nine species of gammarids have been studied in oocytes and embryos. There is no evidence that polyploidy has played a part in gammarid evolution. Three of the species which we have studied, Gammarus pulex (L.), Marinogammarus marinus (Leach) and M. pirloti (Sexton & Spooner) show chromosomal polymorphism. There is no evidence that this polymorphism depends on the existence of a Robertsonian ‘fragmentationfusion’ system; rather it appears to be due to the presence of supernumerary chromosomes.

From July 1955 to June 1956 a study of host-parasite relations between three species of marine fish and their Protozoa was made at Plymouth. Callionymus lyra, a bottom-dweller, tends to be more abundant during the summer months, consumes a wide variety of food, and was more heavily infected with Protozoa than were the other two species offish. Gadus merlangus is an active predator, feeding on small fish, and although it has about the same numbers of kinds of Protozoa as does C. lyra, it was less heavily parasitized. G. merlangus, however, was more heavily parasitized with worms than were the other two fish. Microstomus kitt is a sluggish bottom-dweller, feeding on annelids, and, although over 99% were infected with myxosporidia, the intensity of infection was generally low. Very few other parasites were found in M. kitt.

An active predatory habit combined with a taste for a wide variety of food appears to predispose to heavy parasitism. Some evidence for seasonal variations in intensities of protozoan infection in Callionymus lyra was obtained, but for conclusive results more precise methods of measuring numbers of parasites, and further studies carried on over a period of at least three consecutive years, must be made. The report is presented primarily to emphasize the importance of an ecological approach to the study of parasitology.

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.

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.

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.