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 breeding of Patella depressa was studied at Trevone, North Cornwall, for 4 years. Gonads were examined and assessed by methods described in a previous report on P. vulgata.

In contrast to the common Limpet, P. depressa is a summer breeder in Cornwall. Gonad development begins in the spring and is complete by June or July. Spawning coincides with maximum air temperatures in July, August or early September. The autumn and winter period is passed with gonads in recognizable post-spawning and spent stages, and only a small proportion of completely resting neuter gonads is found in the early spring.

Mass spawning takes place, and gametes are voided rapidly. No definite spawning stimulus can be shown, but, as with P. vulgata, there may be some relation between onset of spawning and the occurrence of wave action on the shore.

The differences in breeding behaviour of P. depressa and P. vulgata reinforce the other differences between them and throw some doubt on the concept of super-species in Patella.

With the exception of a few specially designed models, most under-water cameras today employ no means of pressurizing, or at best merely have a Schrader valve fitted to the case which can then be pressurized, prior to each dive, with a few strokes of a bicycle pump. This method has one severe drawback in that the majority of camera cases are better able to withstand external rather than internal pressure. The chances of a case exploding or blowing a gasket while pressurized prior to a dive are far greater than those of implosion of a non-pressurized case in a comparable depth of water.

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 tellinid Macoma balthica moves extensively about the surface of the sand, its activities not being restricted to vertical movements as hitherto supposed.

These horizontal migrations comprise a movement towards the sun followed by a movement away from it. If there is heavy cloud movements still occur, in summer at least, but are at random.

Other intertidal species indulge in similar movements, possibly indicating a widespread habit which confers the advantage of bringing the animal into contact with surrounding areas while maintaining its station on the shore.

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.

Sea water from the Plymouth district and sea water from the Firth of Clyde each produced, from the same batches of fertilized eggs of Echinus esculentus, a different morphological type of larva. Each type was clearly recognizable irrespective of the copper concentration up to a level higher than that ever likely to be found naturally in the localities from which sea waters contrasted in earlier experiments had been obtained. Suggestions by continental workers that these earlier results may have been due to varying copper concentration are thus shown to be inapplicable.

The variation in convexity of the valves and the development of the pedicle opening in M. echinata is described in shells from a length of 1·2 mm to 13·5 mm and it is concluded that the differences in shell shape and form of the pedicle opening between M. truncata and echinata are of no more than specific value and that the latter species should be transferred from Pantellaria back to Megerlia.

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 ninhydrin-positive patterns produced by chromatography of foot tissue of Nassariics reticulatus from Plymouth and North Wales and of specimens of Nassarius from Essex were established. The similarities and differences between the two are described and the consistent differences found are considered to be indicative of genetic differences between the specimens from Essex and those from the other two areas. The only factor found to affect the otherwise remarkably reproducible pattern given by individuals from the same area was the degree of starvation; the effect was reversible. The pattern given by another marine gastropod, Littorina littorea (L.), is also described. Reference is made to the potentialities of the technique.

Megerlia truncata and M. echinata dredged by R.V. ‘Sarsia’ have been examined living. The growth stages of the lophophore are described and figured, the series being fuller in M. echinata than in M. truncata. The adult lophophore of M. truncata has been sectioned and its structure described.

The ciliary feeding mechanism in Megerlia is similar to that already described by the author in brachiopods with plectolophous lophophores

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.

In the common sole Solea solea retinomotor changes take place. The retinal pigment usually expands in the light and cones shorten; reverse changes take place in darkness.

An account is given of the mortality of Ostrea edulis at the Tal-y-foel oysterage from 14 days to 11½ years after metamorphosis. In the first year after settlement most of the deaths occur in the late summer, autumn and spring, and few during November-February. A survival curve has been drawn up and shown to correspond with Pearl's ‘positive skew rectangular type’. On the average, from 1000 14-day-old spat, 78 survive for 6 months, 18 for 18 months and 7 for 11 ½ years. At this oysterage the major predators are rare or absent, and the cause of most of the mortality is unknown.

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.

Evidence from animals dug up on the shore, from observations on burrowing, or from shell shape indicates that the following species normally lie below the surface with their right valve uppermost: Tellina squalida, T. tenuis, T. fabula, T. donacina, and Arcopagia crassa. Information on the habits of the remaining Tellinidae has not been obtained.

Animals placed on the surface of the soil with the left side up turn themselves over as they burrow. In Arcopagia the shell is turned over beyond the vertical before the animal enters the substratum, but in the remaining species studied the shell is gradually turned over so that it disappears below the surface almost vertically and subsequently completes the turning movement beneath the surface.

The disposition of the siphons of Arcopagia may differ somewhat from that of T. tenuis as described by Yonge, and there is a need for further observation on the siphons of the other species.

Two forms of Venerupis rhomboides occur in Plymouth waters. A more slender form, corresponding to that described by Pennant, occurs in the Eddystone shell gravel, and a more robust form, corresponding to the Venus sarniensis of Turton, occurs at the mouth of the River Yealm. The two forms differ in ratios of shell height, width and lunule width relative to shell length. A population with intermediate ratios is found at 6-5 m in Plymouth Sound.

Plots of height/length ratios of these and another intermediate sample on probability paper did not indicate that the intermediate populations were composed of mixtures of the two extreme forms, and it was provisionally concluded that these were all variants of a single species.

If the height/length ratios of series of samples from different localities are plotted against depth of water on a logarithmic scale, an inverse relationship, approaching a straight line, is obtained. Regression lines for median ratios in the 3-4 and 4-5 cm length groups have been plotted separately, as there is some change in proportion with increasing length. These show a highly significant negative correlation between shell ratios and depth.

From the regression lines it has been possible to obtain an estimate of the depth inhabited by even quite small samples of shells. Depth estimations have been made for eight samples, consisting mainly of dead shells. Six samples lay within the expected limits, and discrepancies in the other two samples are attributed to transport along the sea floor.

The possible causes of the differences in shell ratios are discussed. Previous work suggests that shell ratios may be affected by different rates of growth. Soil grade, temperature, food supply, and light penetration are considered unlikely causes of the observed differences in shell ratios, and it is suggested that the pattern of growth may be affected by pressure.

The Appendix contains a key to British species of Venerupis.

Lichina pygmaea failed to recolonize areas cleared from within the lichen ‘mats’ after four years. A retrogression of the lichen was observed in some instances over periods of 5–7 years. A complex of factors governs the size reached by a lichen tuft; more rapid growth occurs in regions where there is some moisture retention during tidal periods. Although changes occurred with individual ‘patches’ of lichen, the total Lichina cover on a rocky surface remained much the same over a 7-year period.

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.

Macerated tissues of whole Arenicola marina, when injected into the body cavity of male worms, induce spawning after a prolonged latent period of, generally, 60—90 min. The nature of the spawning reaction is described. Emulsified tissues were submitted to heat, ultra-filtration, extraction by fat solvents and saponification. The technique is described whereby the products of these treatments were assayed for potency in inducing the spawning of male worms. The active substance proved to be a lipid and upon rigorous saponification the fatty-acid fraction was found to induce shedding, but the unsaponifiable fractions failed to do so. The active substance was also found to be a normal tissue constituent of male, female and immature worms, but it is concentrated in the gut and coelomic contents. Tissue extracts appear to induce spawning primarily by the breakdown of the sperm morulae in the coelom to free spermatozoa, but there may also be some modification of the action of the nephromixia. It is suggested that the active substance found in the tissues provides the ‘internal stimulus’ by which spawning is normally induced. Evidence for this suggestion is that it is derived from the tissues of the worm and that it appears to be a specific chemical fraction of the tissues which is effective. In addition, tissue extracts induce a normal spawning reaction and there appears to be a relationship between the temperatures at which the active substance is most potent in inducing shedding in the laboratory and those prevailing on the shore during the breeding season. The possible mode of release of the active substance is discussed.