Worms for dissection, or for museum preservation, should be prepared by the magnesium-formalin method, of which two modifications are given in the text.

The body of Arenicola is differentiated into: (a) an achaetous ‘head’, comprising the prostomium and a small number (probably two) of subsequent segments, (b) a ‘trunk’, composed of a number, varying somewhat with the species, of chaetigerous segments, and (c) a ‘tail’, which may or may not be chaetigerous according to the species. The method of subdividing the body according to the distribution of the gills, so often met with in the literature, is misleading because it conceals the very fundamental differentiation between ‘head’ and ‘trunk’.

The main layers of the body wall are described. There are grounds for supposing that the circular muscle layer plays a greater part than the longitudinal in the maintenance of a postural fluid pressure in active worms.

A population of the lamellibranch Tellina tenuis in the Exe estuary is shown to be uniformly distributed, indicating a significant degree of ‘over-dispersion’.

By plotting the position of each shell in squares of m.2 area it is shown that fewer individuals than would be expected occur less than 1 in. from their nearest neighbour, and none occurs closer than 0·6 in.

When the population density was artificially increased on the shore the same characteristic spacing was found at a moderate density, but not at a rather higher density.

It is suggested that spacing is correlated with the foraging activities of the inhalent siphon on the soil surface.

Very dense populations have been found by Stephen in other areas, indicating that the size of the ‘territory’ does not limit density. His results show no evidence of the same phenomena as observed in the Exe.

The seasonal variations in the total ash, crude proteins, mannitol, laminarin and alginic acid contents are given for monthly samples of the Laminariaceae, L. cloustoni, L. digitata and L. saccharina from November 1946 to October 1948, samples of L. digitata and L. saccharina having been taken at different localities to determine the effect, if any, of the degree of exposure on the chemical composition.

The results agree favourably with those of the first 2 years examined and indicate that, with only a few exceptions, results might be reproducible in the corresponding season of any year, and it should be possible, therefore, to predict the approximate composition in subsequent years.

As before, the marked seasonal variations in chemical constitution occur in the fronds, where the bulk, if not all, of the photosynthesis occurs. The stipes undergo some variation parallel to that in the fronds, but within narrower limits, while laminarin is absent throughout the year.

A gregarious tendency during settlement, similar to that already demonstrated in oyster larvae, was suspected in Elminius, because cyprids settled in groups during the initial stages of colonization of surfaces (crowded later arrivals showed a spacing-out tendency) and because settlement on test-plates was peculiarly sparse at stations with a muddy bottom, where barnacles were absent.

Settlement was much heavier on areas of smooth glass, which already bore recently settled barnacles, than on similar adjoining areas which were bare.

When barnacled microscope slides were stuck to one set of glass plates, bare slides to another and the two sets exposed side by side, settlement was consistently much heavier on the plates which bore the barnacled slides. The mean density of settlement on the bare slides and the surrounding plates was uniformly low, except for a greater density immediately adjoining the slides, probably due to sheltering alongside their edges. On the barnacled slides density of settlement was much higher and on the plates immediately alongside still more so, whilst at increasing distances from the slides it became gradually smaller but was still much heavier than on the plates with the bare slides. This suggests that the sensory basis for gregariousness can act at a distance. It may possibly be olfactory.

Cerithiopsis tubercularis and Triphora perversa feed on siliceous sponges: a long proboscis is thrust through an osculum of the sponge, or into breaks in the surface, to reach the softer parts. These are loosened by jaws, entangled in saliva and swept into the buccal cavity by the radula.

The formation of a long introvert, which must be withdrawn through the narrow space in the nerve ring and narrow enough to go through an osculum, has brought about (i) a lengthening of the mid-oesophagus in Cerithiopsis, with a narrowing of its diameter, and a spreading of the oesophageal glands along its length, (ii) in Triphora, a reduction of the ventral glandular part of the mid-oesophagus, its stripping from the food channel and a displacement of the salivary ducts so that they open into the glandular part of the oesophagus. In Triphora there is a dorsal gland of unknown function on the posterior oesophagus.

The stomach in both species is a simple ciliated sac: the oesophagus opens anteriorly and ventrally, and the intestine originates above this opening; there are two ducts from the digestive gland.

The pallial region of the male and female genital duct is open; and there is no penis. It is suggested that the open condition of the duct and the absence of a penis in the mesogastropods is correlated with a long, narrow mantle cavity which contains a relatively large ctenidium.

A review is given of the results obtained from upwards of 600 days of current measuring at the Seven Stones lightvessel during 1939–41. From the plotted observations, an attempt is made to deduce the association between the total daily water movement, irrespective of direction, the residual daily water movement or current, and the mean local residual wind.

The average residual water movement over the whole period was 2½ m.p.d. towards east-south-east. Statements made by earlier authors regarding the water circulation in adjacent areas are examined, and reconciliations are suggested where they seem to conflict with this finding.

An endeavour is made to correlate the wind and water movement mathematically.

A series of results is presented on the barnacle larvae population of an area of the Firth of Clyde, over a 15-day period in the spring taken by means of a modified Hardy Plankton Recorder.

The records and observations on barnacle settlement indicate that the larval population was considerably greater than usual.

The total larval population showed no great fluctuations from day to day, and on a given day the composition of the population over a wide area was often reasonably constant.

Evidence is presented that there is no great depletion of the population between Nauplius III and cyprid stages. It is suggested that the depletion previously reported may be due in part to the method of sampling or to the conditions at the time of sampling.

During the time when the evidence indicates no depletion of population there was a heavy diatom outburst, which in this instance did not appear to interfere with the larval development.

Data are given on the density of settlement.

A description is given of a glass cloth surface which prevents the settlement of larvae of Balanus crenatus and Pomatoceros triqueter, whilst not affecting that of Tubularia larynx. A number of possible causes for this are examined, and its relation to other work on the settlement of sedentary forms is briefly considered.

Norman (1905) gave a short account of the distribution of the ophiuroid, Ophiopsila annulosa, having dredged it himself from Birterbuy Bay, Ireland, in 1874, and from outside Dartmouth Harbour in 1904. He also obtained specimens in 1903 from the Plymouth Laboratory; these had been dredged in 12–25 fathoms on Mewstone Ledge and Stoke Point Grounds, near Plymouth, and were recorded as not uncommon in the red sandstone, especially in old Pholadidea crypts. Mortensen (1927) expressed some doubt as to Norman's identification of the Irish specimens; he noted that the Plymouth specimens had been found in exactly the same locality and habitat as the smaller and commoner species, Ophiopsila aranea, and considered that the presence of the larger species in British waters could not be definitely settled until new records were to hand. O. annulosa was not recorded in the Plymouth Marine Fauna (Mar. Biol. Assoc, 1931) and no specimens have been found in the reference museum at the Laboratory.

In Branchiomma vesiculosum decrease in light intensity causes the animal to contract and withdraw into its tube. A decrease, never an increase, in illumination is the effective stimulus. When repeatedly stimulated the animals quickly become adapted to intensity changes and no longer respond.

The minimal effective intensity change has been determined for a range of intensities. ΔI/I is found to increase in low light intensities, and to be fairly constant in intensities over 50 lux. The animals are least sensitive to red light; sensitivity increases in shorter wave-lengths.

The pigments of pure cultures of algae, of known number per volume, have been extracted with aqueous acetone after separation by filtration. The extracts were compared in a Kober colorimeter with standard solutions of a preparation of bought chlorophyll. The number required to give 1 mg. of chlorophyll was thus determined.

The algae studied included: Chlorophyceae, two species of Chlamydomonas and one Chlorella not yet described; Chrysophyceae, Dicrateria inornata Parke; Bacillariophyceae, Coscinodiscus centralis Ehr., Thalassiosira gravida Cleve and Nitzschia closterium (Ehr.) W.Sm. forma minutissima; Cryptophyceae, Hemiselmis rufescens Parke; Dinophyceae, Gymnodinium sp. The numbers per milligram of chlorophyll varied from 74 × 103 for Coscinodiscus to over 3200 × 106 for Hemiselmis rufescens. Of the nine cultures, six were between 50 and 750 × 106. The volume of the cell is the decisive factor in the milligram count.

The parasitic astomatous holotrich ciliate, Orchitophrya stellarum Cépède, has been found in the testes of starfishes (Asterias rubens) in the Plymouth area. It was found only in starfishes from numerically rich and well-fed populations, which also showed large gonad growth. In such populations it occurred in up to 28% of the males during March-April 1947, and in lower percentages during the spring of the three following years. The parasite was never found in a geographically adjacent population containing smaller numbers of poorly fed starfishes. The parasite was found to be relatively more common in the testes of medium-sized starfishes than in those of large and small starfishes.

Presence of the parasite causes a complete breakdown of all the germinal tissue of the testes, so that most of the infected starfishes suffer complete castration. This involution of the testicular tissue has been studied, and photomicrographs are given which show a number of stages in the process.

An account is given of the reproduction and development of the larva of N. diversicolor O. F. Miiller.

In any one population the number of males was found not to exceed 10 %.

The species is dioecious. Both sexes become green at maturity, but may be distinguished externally.

Ripe oocytes, which vary between 200 and 250μ in diameter mature in a loose coelomic parenchyma, and are released by rupture of the body wall after its partial histolysis. Sperm is released through the nephridia, or possibly by rupture of the body wall as well. In the male histolysis occurs, but the coelomic parenchyma is transitory. Sperm matures in the form of coelomic sperm plates.

Gymnammodytes semisquatnatus, the North Atlantic smooth sand-eel, has a continuous distribution from southern Norway to the southern Atlantic coast-line of Spain. Its occurrence in the Irish Sea and in the Plymouth area are new records. In the latter area it is an off-shore species, apparently concentrating in shell gravel in winter for spawning. It has a mean vertebral number of slightly over 68 (Plymouth and Scottish specimens). A small sample of the Mediterranean species, G. cicerelus, gives a mean of just over 66, while the South African species, G. capensis, which is indistinguishable from G. semisquamatus by external non-metameric characters, has a much lower mean of 58·5.

The pilchard, Clupea pilchardus Walbaum, is known to spawn in summer in the southern North Sea in the neighbourhood of the Sandettié Bank (Buchanan-Wollaston, 1911; Furnestin, 1939a, 1945) and in the eastern English Channel off Beachy Head (Furnestin, 1939a, 1945). Furnestin (1939b, 1945) concludes from these records that spawning is in all probability continuous throughout the Channel from the southern North Sea to the Celtic Sea. There appear, however, to be no previous references to pilchard spawning in the central part of the English Channel. The following records from the area are of interest therefore, and provide confirmation of Furnestin’s conclusion.

The genital products of Saccoglossus horsti are discharged within the burrows and expelled after the tide has ebbed. They are not retained in the burrows for any length of time.

Fertilization occurs mainly in the overlying surface water, or during the flood.

An ‘epidemic’ spawning was observed on three occasions in the field.

A rise of temperature to about 160° C. is regarded as the essential factor primarily responsible for initiating the spawning.

The females were observed to spawn before the males. Some reciprocal inducement might have occurred.

The breeding season in the Solent area is mainly confined to the months of May, June and July, and is seemingly dependent on climatic and tidal conditions during these months.

The spawning behaviour of other species of the Enteropneusta is discussed.

In Britain Octopus vulgaris occurs on the Channel coast and only very rarely on other coasts. In Brittany and the Channel Islands it frequently makes its lair at low water, but on the English side of the Channel it does not come so close inshore except in abnormal years of high sea temperatures.

The discovery of Octopus larvae of various sizes, from newly hatched to 6·0 mm. (mantle length), in plankton hauls taken to the north of the Channel Islands, proves that the species has a much longer planktonic life than hitherto supposed.

The water circulation in the English Channel, as indicated by drift bottles, is admirably suited to the dispersal of larvae to our shores from breeding centres on the coasts of Brittany and the Channel Islands.

A study, now in progress, of the phosphorus cycle in the sea off Plymouth required some knowledge of the amount of plants and of several ecological groups of animals. There were no existing data except for zooplankton and the larger net-caught phytoplankton.

From information supplied by friends and colleagues, it was possible to make tentative estimates of the average biomass of other groups of animals occurring below unit area of the sea.

The diagnostic characters of the British species of Ensis are described. The shell remains the primary means of identification, but additional characters in the soft parts are necessary for certain recognition. The three forms of Ensis described are considered to be valid species.