The dependence of prevailing wind drift in the Celtic sea upon prevailing winds is discussed and a proposal made to use wind records for the Scilly Meteorological Observatory for assessing drift currents for use in biological investigations.

If there is no seasonal change in the direction of the prevailing winds, nevertheless, the wind drift in summer will be more northerly than in winter.

The terms ‘current’, ‘residual water movement’ and ‘drift’, as used in this series of papers, are denned. The Ekman–Thorade equation for computing wind drift from wind is discussed and applied to the drift of the biological indicator Muggiaea atlantica in 1938. The two approaches agree to suggest that either method may be applied in biological distribution studies.

Some effects of drift, due to variable winds, on plankton distribution are outlined.

The circulation of the northern and north-eastern Celtic Sea, has been studied, using especially observations made in April 1950.

The Celtic Sea in that month was 0·5° C warmer than the average temperature 20 years earlier.

The following distinctive water masses have been recognized (i) Land's End water; (ii) South Wales coastal water; (iii) Carnsore corner current water; (iv) Nymphe Bank water, including a component enriched by up-welling off Waterford; (v) County Cork eddy water.

The South Wales coastal water, though rich in nutrients presumably derived from sewage effluents, was not very productive. A parallel is drawn with the Hyperion sewage scheme of the City of Los Angeles.

The low-salinity water present in the centre of St George's Channel in summer is attributed to flow from the coast of South Wales. In the autumn water is recruited more directly from the Celtic Sea.

The silicate content of the Carnsore corner current was half that in South Wales coastal water on the opposite side of the Channel.

Up-welling of water enriched by breakdown of bottom muds occurred off Waterford.

The drift system in the central Celtic Sea is dominated by the prevailing winds. The drift in April 1950 was a composite affair and it has been possible to dissect some of the components and to show how they interplay.

In about 7° W. long., a mixed water mass sets south from the Nymphe Bank and was identified for more than 100 miles.

A tentative explanation is offered for the distribution of compounds of phosphorus in terms of regeneration from bottom deposits.

Tapeta were examined of light- and dark-adapted dogfish. Scyliorhinus canicula. The tapetum in the eye of this fish is fixed; pigment processes in the tapetum do not move when a fish is changed from dark to light and vice versa. A black ventral field and a bright dorsal fundus are always present.

Details are given of the culture apparatus and methods found successful for the laboratory culture of species of Ectocarpus. In attempts to obtain uni-algal cultures of this genus several common methods were tried but only one of them, a modification of the plating technique, proved successful. Methods of washing and dilution were unsuccessful in giving bacteria-free cultures, presumably due to bacteria closely adhering to the cell walls. Ultraviolet irradiation was also unsuccessful but treatment with penicillin gave bacteria-free cultures of E. confervoides and E. secundus (Giffordia secunda).

The growth and nutrition of Ectocarpus confervoides has been studied in bacteria-free cultures. Growth was estimated by dry weights determined under controlled conditions. A method for inoculation of cultures of filamentous algae is described and a table of culture media is given. Following a lag of 5–7 days there was a period of growth, which was not truly exponential, extending over a period of 35 days. Calculation of the relative growth constant for the early stages of growth indicated that the alga doubled its dry weight every 6–7 days. Cultures of Ectocarpus remained viable for over 1 year in the light and for over 100 days in the dark. In natural sea-water media the maximum growth was brought about by the addition of 0·5 mM potassium nitrate and 0·1 mM potassium phosphate. Ferric chloride had no effect on growth but additions of manganese chloride did cause some stimulation. Additions of some complex organic mixtures slightly increased growth but Ectocarpus was unable to grow on a range of organic carbon source in the dark. The optimum salinity at 20° C was somewhat higher than that of natural sea water but was apparently lower at 15° C. The optimum pH was 8·0. Light intensities between 1350 and 16,000 lux had no marked effects on the growth rate but did effect the lag, the optimum for this being 7000 lux. Temperature also had no effect on the growth rate but did effect the lag. The optimum was 15–20° C but there was growth between 10 and 25° C. A considerable range of artificial sea waters, with and without organic additions was investigated, in no case did they give a yield greater than two-thirds that in natural seawater media. These results are discussed in relation to other workers findings.

The numbers of fish eggs and planktonic stages of fish taken during a 5-year period by the Scottish research vessels in the northern North Sea have been associated with the presence of Sagitta elegans and S. setosa in the same collections and over an 11-year period with the presence or absence of S. elegans. The results confirm Russell's findings in the English Channel that fish larvae are more abundant when S. elegans is present than when S. setosa is present.

The total numbers of fish eggs do not show these differences; spawning does not appear to be any more productive in water associated with S. elegans, rather the reverse, and this is shown to be so for the eggs of those species separately examined. Numbers of the larvae were distinctly greater in the ‘mixed’ conditions indicated by the presence of S. elegans and a more abundant food supply is a possible cause. That the differences may signify a more fundamental effect, however, is suggested by the figures for cod and haddock eggs, which show the earliest stages to be more abundant where S. elegans was absent although later stages were more abundant when S. elegans was present.

The spectral absorption of the violet pigment extracted from dried Ianthina secretion by acetone is described. The colour of the secretion adsorbed on cellulose tissue is reasonably stable for purposes of transport. The pigment does not appear to be identical with the bilidiene-protein pigments of Aplysia, or with other violet molluscan pigments. The pigment of Ianthina shell is not extractable with acid, and all save that of the pellicle disappears on decalcification.

The excess weight in sea water of the living tissues of Sepia officinalis (L.) is approximately balanced by the cuttlebone, which accounts for about 9·3% of the animal's volume. The density of cuttlebone varies around 0·6. The cuttlefish without its cuttlebone would be about 4% denser than sea water.

The chambers of the cuttlebone are independent of one another but liquids and gases are free to move within any one chamber.

Animals caught and studied fresh aboard ship exhibited a much less wide range of cuttlebone densities than those kept in an aquarium.

Specimens kept in aquaria vary greatly in buoyancy. These variations result from changes in density of the cuttlebone.

Cuttlebones differ not in the weight of dry matter per unit volume, which is always close to 38%, but in the amount of liquid they contain. A cuttlebone of density 0·7 contains about 30% liquid whereas a cuttlebone of density 0·5 contains about 10% liquid. The remainder of the cuttlebone contains gas, but this gas is at less than atmospheric pressure. The pressure of gas varies around 0·8 atmosphere. Within the duration of the experiments described here, the mass of gas per unit volume of bone remained almost constant whatever the bone's density. The pressure of gas is lower the less dense the cuttlebone. There can be no question of an evolution of gas expelling liquid from a bone when it becomes lighter. The constancy of the mass of gas within the cuttlebone is explained in terms of the slowness of diffusion of gases into the bone.

The behaviour of well fed cuttlefish is strikingly affected by light. When the light is bright they usually bury themselves in the gravel at the bottom of their tanks, whilst after twilight they come out of the gravel and swim around until dawn.

Cuttlefish kept in complete darkness for one to two days usually become so buoyant that they are incapable of staying on the bottom and can only remain in mid-water with difficulty.

Animals kept in artificial light and dark showed changes in density which could amount to 2%. These changes come from changes in the volume of the gas space within the cuttlebone.

The density of the cuttlefish is largely governed by light intensity and there is little indication of an inherent diurnal rhythm of density change.

The rate of uptake of liquid when the cuttlefish becomes denser is such that it is unnecessary to assume that any active process is used to pump liquid into the cuttlebone. The cuttlefish must, however, extract liquid actively from the cuttlebone to become less dense.

Experiments are described which test the hypothesis that the cuttlefish controls the relative volumes of gas space and liquid within its cuttlebone by an osmotic mechanism acting across the siphuncular surface of the bone. When the animal is at the bottom of the sea it would maintain the gas space within the cuttlebone by balancing the hydrostatic pressure of the sea by an osmotic force between the liquid within the cuttlebone and the blood.

In cuttlefish kept for some weeks in shallow water in an aquarium all the liquid taken from the cuttlebone is almost isotonic with the animals’ blood.

In animals recently hauled from the bottom of the sea the cuttlebone liquid is markedly hypotonic to sea water and hence to the blood.

These lower osmotic concentrations are given chiefly by reduction in the concentrations of the sodium and chloride ions.

After bringing animals up from about 70 m to the surface of the sea the osmotic concentration of the cuttlebone liquid rises from about 75% of sea water some 40 min after starting to haul the trawl, to about 97% of sea water 6 h later. Extrapolation back to the time at which hauling began gives a concentration of salts close to that predicted by the osmotic hypothesis.

Whilst the cuttlebone liquid is increasing in ionic concentration the liquid deeper in the cuttlebone is hypotonic to that just inside the siphuncular surface. This is explained in terms of the slowness of exchange of salts along the narrow channels between the lamellae of the cuttlebone.

The newest chamber of a cuttlebone is always incomplete and full of a watery solution. This contains sodium and potassium in concentrations close to those of sea water.

The second newest chamber contains a gas space and sometimes contains liquid. This liquid is rarely localized at the siphuncular end of the chamber. It is not certain that liquid is initially extracted through the siphuncular wall of the chamber, although this is possible.

When liquid is pumped out of a newly formed chamber the salt which it initially contains is not left behind, either free or bound into the structure of the bone.

The 3rd to about the 10th newest chambers usually contain no visible liquid. But their siphuncular walls are permeable to liquid and liquid does enter these chambers when the cuttlebone becomes very dense.

At cuttlebone densities around 0·6, i.e. close to values which will make the cuttlefish neutrally buoyant, the older and more posterior chambers are almost full of liquid. This liquid can, however, be pumped out. When a cuttlebone has a density around 0·5 very little liquid can be seen in any of its chambers.

The pressure of gas within a newly ‘pumped out’ chamber is very low, but by the time a chamber has become the ninth newest the pressure of gas is close to the average value for the whole cuttlebone, i.e. about 0·8 atm.

The low pressure of gas found in the newest chambers is explained by the slowness with which gas diffuses into a space created by the active removal of liquid.

The germ cells of Polydora ciliata arise from cells lying just inside the ventral epithelium and later migrate into the gonads. They are released into the coelom when they are 30 μ in diameter and are transported posteriorly to the region of maturation. The eggs and sperm are shed through the modified nephridia of the region of maturation. The eggs are laid into a string of capsules apparently secreted by the nephridia and attached to the wall of the tube. The larvae take about a week to hatch and are released into the plankton at the three chaetiger stage. They spend some 6 weeks in the plankton before metamorphosis, and have grown to 17 or 18 segments. Monthly samples of the worms living in the London clay at Whitstable in 1956 showed that the population was bimodal with respect to size and the two groups of adults gave rise to two larval settlements in late March and May. The two groups of juvenile worms that developed from these larvae retained their identities through the summer and the following winter. There is no apparent morphological character by which the adults of each type may be recognized, the time of spawning and the lower fecundity of the early breeding worms being the only distinguishing features. It is suggested that these groups are the consequence of an overlap of two populations of P. ciliata from different centres of distribution, each being adapted in its breeding requirements to a different part of the temperature range.

A survey has been made of the bottom fauna in ca. 10–50 m along the south coast of England, using a modified anchor-dredge. Particular attention has been paid to the molluscs (both living and dead) and to the echinoderms, only larger or more conspicuous members of other groups being identified.

Within the Channel there are considerable variations in temperature and other hydrographic conditions, and these are discussed in relation to their possible role as limiting factors in distribution. The fauna and bottom deposits of the different areas covered in the survey are briefly described.

Distribution trends are classified as:

(1) Species generally distributed in the Channel. This is the largest group, and includes three species reaching their northern limits in British waters.

(2) Species confined to the western parts of the Channel.

(a) Western species. Four or five species common at Plymouth in the 1920's, but now absent or very rare. Small numbers are found today only off the south Cornish coast, and those which occur in the North Sea are restricted to the north-western areas. Apart from one species, these forms are not at their geographical limits in the English Channel, and their occurrence may be partly related to the presence of ‘western’, but not necessarily Sagitta elegans, water.

(b) Cornubian species. These are near the northern end of their range, and occur quite commonly off the south Cornish coast, becoming progressively less common farther up-Channel. It is suggested that their distribution is related to an intolerance of the lower winter temperatures in the more eastern part of the Channel.

It is shown that equilibrium of 32P throughout the body of Calanus is reached only after a feeding period of about a week. The time required to liberate by excretion the amount of P present in a Calanus is about 20 days. Fed Calanus excrete at a higher rate than starved. The implications of excretion in feeding experiments using 32P is discussed.

There are large differences in the total P content of individual Calanus. Figures are given for ripe and unripe females, fat and lean Stage V, and eggs. A high percentage, up to 55% of the total P, may be lost by excretion during starvation.

A high proportion of the P in the food assimilated (up to 70%) may appear within a week as eggs laid.

Liberation of P from dead Calanus is very rapid and is almost complete in three days.

The relation of excretion and autolysis to the P cycle in the sea is discussed.

The functional morphology of twelve British species of the Veneridae is described. The systematic position of Mysia undata and evolution within the Veneracea are discussed.

Structurally, the members of the family Veneridae show a lack of special adaptations. The ability to move horizontally as well as ventrally in soft substrata is retained; the pedal gape is large and the foot well developed. The siphons are relatively short and fused. The food-collecting mechanisms of the mantle cavity are largely unspecialized and function in maintaining a considerable flow of water, and retaining as much as possible of the suspended material. Members of the Veneridae show a considerable uniformity of structure, but trends of evolutionary change may be distinguished. The genera Gafrarium and Callista are least specialized. The genus Dosinia has evolved along an independent line and is specialized by the possession of a stream-lined, circular shell, deep lunule, and greatly elongated siphons, for a relatively deep-burrowing habit. Within the superfamily Veneracea major lines of adaptive evolution have given rise to the rock-boring Petricolidae and the deep-burrowing Glaucomyidae, and the genera Venerupis and Irus show affinities with both these families.

Chrysochromulina minor and C. kappa have been re-investigated by means of electron microscopy of thin sections to add details of the microanatomy of pyrenoids and haptonemata, and by anoptral contrast light microscopy to study pyrenoids in living cells. In both species the pyrenoid is in the form of a diverticulum projecting from the centre of the inner face of a plastid and, in C. minor, strongly flexed to lie along it. In C. kappa the pyrenoid is commonly enveloped by the nucleus which may conceal it entirely from view in life. Some details of the behaviour of the surface membranes of plastids and pyrenoids in relation to that of the nucleus are given. The haptonema structure in both species is shown to be comparable to that of others in which this appendage is much longer, though an occasional variant with eight instead of seven central fibres or tubes has been encountered in C. kappa and is demonstrated. The presence of ‘peculiar’ Golgi structure is reported for both species and demonstrated for C. kappa. Some direct evidence indicating an internal origin of scales from vesicles is demonstrated in C. minor. Finally a summary is given of salient structural criteria for all the described species attributed to this genus from the marine plankton, the closest agreement as regards pyrenoid structure in the two species under investigation being with C. chiton.