Continuous observations on the Upper Fal Estuary oyster beds during the years 1925, 1926, and 1927 have established the fact that 0. edulis exhibits on these beds two definite periods of shell-growth, i.e. increase in shell-area, in one year; one period of general shell-growth occurs in the spring, beginning early in April, and the other in autumn at the end of September or early in October. There is some evidence-but as yet incomplete-that internal shell-growth occurs solely and simultaneously with the deposition and thickening of the new shell-shoots in a period of one to two months.

These general bursts of shell-growth occur in the pre-breeding and post-breeding part of the season

Similar periods of shell-growth occur on beds in the River Blackwater (AVest Mersea), and also occur mainly in the pre-breeding and postbreeding part of the season; but shell-growth begins in the spring in April-May on these beds, a few weeks later than on the Upper Fal Estuary, and in the autumn in August-September a few weeks earlier than on the Upper Fal beds.

Spring and autumn periods of shell-growth are also known to occur on many other estuarine beds.

The Marine Biological Association of the United Kingdom, to whom the Plymouth Laboratory belongs, is a corporate body of subscribing members, interested in scientific investigations concerning the habits and life-histories of food fishes and other marine animals. The Laboratory is managed by a Council elected annually by the members of the Association.

The genus Edwardsia is one known to most zoologists as an example of a primitive eight-rayed Zoantharian from which (or from a form resembling which) the higher forms are derived. It is only comparatively recently, however, that our knowledge of Edwardsias has become at all extensive, and even now it is incomplete; but it is desirable to produce a revision of the British forms since no adequate account of these exists.

The vertical distribution of Calanus finmarchicus adults in the daylight in the Plymouth region as shown by stramin ring-trawl catches in described for the period April to September in 1926. The general results confirmed the indications given in 1925 that there is a, gradual descent of the region of maximum abundance from about 10 metres in April to-metres in June, with a definite rise towards the surface ia July, August, and September.

2. The rise towards the surface was evident on sunny days as well as dull, indicating that the suggestion that dull weather and low light intensity was its cause in 1925 may possibly have been incorrect.

Measurements of the total lengths of Calanus were made which showed a seasonal change, a brood of small adults occurring in July, August, and September, as opposed to a brood of large adults whichdominated in the spring.

It is suggested that possibly these two broods are physiologically different, and that the small type of adult prefers a higher light intensity and lives nearer the surface than the large type.

The males and females differed in their behaviour, the males being always slightly deeper in the water than the females.

Some indications are given of the course of the life-cycles of Calanus in the Plymouth area.

While from April to the end of June the abundance of the last copepodid stage (Stage V) rarely exceeded more than 20% of the total Calanus in any one catch, they became very much more abundant in July, August, and September, reaching even 60% and 70%.

The following list brings up to date a previous publication and has been classified, so far as practicable, according to subjects, in order that it may be useful for purposes of reference. The list does not include publications recording the results of observations made on material supplied by the Association to workers in different parts of the country, of which a considerable amount is sent out each year.

The following paper has been prepared in the hope that it will be of assistance to anyone desirous of carrying out experiments on Heredity with Gammarus chevreuxi. This Amphipod has been the subject of study at the Plymouth Laboratory since 1912, and the following notes are chiefly concerned with rearing and breeding it under Laboratory conditions.

Details of the work will be found in the papers mentioned in the bibliography on page 54.

Results are given of a further series of collections made with the stramin ring-trawl to determine the diurnal behaviour of post-larval stages of Teleostean fishes in the Plymouth area.

The catches were very satisfactory and showed that in no case, except for Clupeids and Gobies, was there any really marked movement of young fish towards the surface. This confirms previous observations.

It has been shown on this and previous occasions that Clupeids are many times more abundant in the catches at night than in the daytime, and any study of their seasonal or horizontal distribution would probably.have to be carried out at night.

For the remaining species, except perhaps Gobies and Callionymus, oblique hauls taken either at day or at night should give a fair picture of seasonal or horizontal distribution. More observations are, however, required.

The association of the whiting young with the medusa, Cyanea capillata, is discussed.

Thysanoessa raschii is a regular inhabitant of the Firth of Clyde. Adults are found throughout this area, generally in waters not less than 40 fms. deep. Those of large size, 23–25 mm., are apparently consistently found from year to year in Loch Striven in large numbers from October to January within 10 fms. from the bottom in waters of 40 fms. depth. Throughout the rest of the year they occur in small numbers in the tow-nets, and are seldom found at all during the summer months. On one occasion, however, February, 1926, several hundreds were fished in addition to large numbers of Meganyctiphanes norvegica at 40–60 fms. in the Cumbrae Deep.

Further measurements have been made of the penetration of daylight into the sea near Plymouth, photometers containing both vacuum and gas-filled photo-electric cells being used. The effect of obliquity of illumination on the sensitivity of these photometers was large, and has been allowed for as far as possible. The sensitivity of the vacuum cell used in the sea attained its maximum at a wave length of about that of the gas-filled cell at about 4,350. The sensitivity of both to wave lengths greater than 5,500 was small.

It has been shown by experiments formulated upon the conditioned response principle that the blenny, Blennius gattorugine, is able to perceive and to profit by very small changes in its environment. This fish is able to form conditioned motor responses using food as unconditioned stimulus, towards a momentary increase of 0-4C, or more, in the temperature of the surrounding water.

It is also able to form similar conditioned motor responses towards a momentary decrease in the salinity of the surrounding water, of as little as 3 parts per 1000, or towards a change of greater magnitude (up to 37 parts per 1000).

Conditioned responses have been established in the wrasses, Crenilabrus inelops and Labrus bergylta, towards visual stimuli of varying kinds. It appears that these fishes can discriminate after differential training between one or two sources of light, and between monochromatic red, green, yellow, or violet light, but not readily between even comparatively large differences in intensity of a luminous source. These results are those obtained upon dark-adapted fishes. More extensive experiments will be necessary before a final statement is made upon their capacity for colour discrimination.

In 1925 observations were carried out on two consecutive nights, June 17–18th and 18–19th, to study the diurnal changes occurring in the vertical distribution of certain marine plankton animals. Serial hauls were made with the stramin ring-trawl in the manner described in a previous publication (1). The series were so timed that they were made approximately in daylight, dusk, darkness, dawn and daylight on the two days in question. The actual details of the collecting, together with the fishing depths shown by the Admiralty depth recorder, are to be found in a previous paper on the behaviour of young fishes on the same occasion (2).

The small individuals were examined before the height of the breeding season, and there is a probability that many or most of the indeterminate individuals would become male. Hermaphrodite individuals have been observed previously, and in certain samples 10% of the males contain doubtful young ova in the gonad. It is therefore concluded that Patella vulgata is apparently a protandric hermaphrodite, but that the evidence is not yet sufficiently good to prove protandry.

It is suggested that possibly two kinds of male, which may be recognisable by chromosome constitution, may occur, one being pure male and one protandric, and also that sex-change may be controlled by as yet unknown metabolic conditions.

The breeding period is discussed ; it may extend from August to March at Plymouth in different seasons, and spawning may occur within this period. A maximum of spawning appears to occur about January-February. The conditions controlling breeding and spawning in Patella are unknown, and as the course of seasonal shell-growth is unknown, although shell-growth is general at the end of the breeding season, it is suggested that research on the subjects in the future should be combined.

The distribution and activities of animals and plants upon the sandy beach are largely influenced by the special physical factors operating in that environment. The paper is a contribution to the knowledge of these factors.

The tidal ebb and flow, and the resulting alternations of exposure, are the outstanding factors. The extent to which other factors may be operative upon the beach, during the period of ebb-tide, depends upon the vertical distance of the point in question above or below mean sea-level.

Many common limpets Patella vulgata, settled and grew on the cement piles of a new wharf constructed at Plymouth. Each pile or part of this wharf provided experimental material for the determination of the maximum age of the limpets which grew thereon, as the dates of completion were known. It was found that at an age of about one year limpets grew to lengths of 26 to 35 mm. in 1912, and to at least 11 to 27 mm. in 1913 :and at an age of two years to at least 53 mm. in 1911-1913, and to 47-49 mm. in 1912-1914.

The shells were of the mid-tide-level type, and were low, broad, and rather thin. It is considered that such growth in length is unusual, and is correlated with the habitat and favourable climatic conditions. In the same situation in 1913 marked limpets grew from January 27 to September 2, respectively, 20 mm. (from 21 to 41) and 15 mm. (from 38 to 53), and showed arrest of growth in midsummer.

Other marked limpets showed arrest of growth in the winter period, and many at lengths of about 25 mm. an arrest of growth independent of any season of growth. Seasonal shell-growth is discussed briefly ; a postbreeding shell-growing period is general in spring and early summer, but it is not known whether a midsummer resting-period is general among individuals more than one year old. Ad hoc investigations are suggested in combination with work on sex and spawning.

A preliminary notice is given of investigations into the cause of variation in shell-height, wherein it is shown that shell-height is determined probably entirely by the degree of exposure of limpets to desiccation, in such a manner that the drier the habitat the higher the shell is. Limpets submerged at neap tides have a relatively uniformly low shell, those exposed at high-water neaps have a relatively high shell, which is higher in the drier than in the damper situations, apparently irrespective of exposure to wave-action.

In the course of the researches on the vertical distribution of plankton it became evident that a net was needed for sampling the water-layers very close to the sea bottom. While the net had to be efficient in capturing the plankton animals present in those layers, it was necessary that the catches should not be vitiated by the presence of bottom-living organisms which had been stirred up from the sea floor by the net itself.

The presence of living organisms and their metabolic products introduce a further series of biochemical factors into the physical conditions of life on the sandy beach.

The gaseous exchanges of animals and plants lead to changes in the pH of the interstitial waters of the beach, but the calcareous matter associated with the sand acts as an alkali-reserve, preventing undue rise of acidity, and incidentally widening the potential range of carbonassimilation of the surface flora.

Further study of the larval crabs of the Plymouth district has resulted in the elucidation of many more life-histories. Amongst these perhaps some of the most interesting are Ebalia and Pinnotheres. These genera, placed by systematists in widely different groups, resemble one another closely in many details in their larval stages and are here purposely described together in order that a comparison may be made.

The developments of Polydora ciliata Johns, and Polydora hoplura Clap, are described from the egg to a very late planktonic stage in the case of the former, and to young metamorphosed individuals in the case of the latter. Only external characters are described.

In both species the eggs are laid in egg-sacs attached to the wall of the parent's burrow.

The larvae of P. ciliata are released at a stage with three chsetigerous segments and lead a long planktonic life.

The larvae of P. hoplura are provided with special food in the form of yolk-masses ; they undergo most of their development while in the protecting burrow of their parent; are released at a very late stage, and have only a short planktonic life.

The larvae of both species have a complicated vestibule surrounding the mouth, and are provided with special sensory cilia on the head.

The larvae are provided with a special kind of cilia, situated at the ends of every nototroch, which are used to take hold of the long provisional bristles in swimming. This suggests that one of the functions of the long bristles is that, in conjunction with these grasping-cilia, they increase the rigidity of the swimming larva, and hence the efficiency of its driving cilia.

Previous references to Polydora larvae are briefly discussed.

The Cirripede Anelasma squalicola (Lovén) is parasitic on the smooth dogfish, Etmopterus spinax (Linnæus). These fish, which are caught a depth of about 150–180 fathoms, were brought to the University of Liverpool as material for a chemical investigation by Professor Heilbronn and his colleagues. On finding that some of the fish were thus parasitised, Professor J. Johnstone and myself made a study of the general morphology of Anelasma (3).