The breakwater in Plymouth Sound offers a simple case of two adjacent populations ofintertidal organisms subjected to quite different degrees of exposure to wave-action. The other environmental factors, with a few exceptions, are approximately the same each side, and the effects of the wave-action should be clearly demonstrable.

Leptoclinides faeröensis Bjerkan (1905) is a little-known boreal species which has been found only in the Atlantic Ocean (Fig. I). The most northerly record is from a little south of Spitzbergen, the most southerly from 37° 08' N., off the North American coast. It occurs on the coast of Norway and in the Faeroe Islands, but it has not been reported nearer to Plymouth than these two localities. Most records are from deepish waters, though it occurs in the sublittoral zone along the Norwegian coast. It was in this zone, at Looe Island (50' 20' 24“ N., 4 °26' 53” W.) near Plymouth, that we found a specimen of this species growing on a rock about 80 cm. below O.D.—just sufficiently low for it to remain covered by a few centimetres of water at the lowest tide of the year, the equinoctial spring tide.

Milne Edwards (1841) established the genusLeptoclinum for those Didemnidae which possessed a largely expanded common cloacal system. His type of the genus wasL. maculosum which is now placed in the genusDidemnum Savigny (1816). Other species wereL. asperum andL. durum which are now regarded as mere forms ofDidemnum maculosum (e.g. Harant & Vernièeres, 1933); Leptoclinum fulgens which is closely related (see Harant & Vernièeres), if not a mere colour form ofDidemnum maculosum], Leptoclinum listerianum which has been transferred to the genusDiplosoma Macdonald; andLeptoclinum gelatinosum. This last has often been considered synonymous withDiplosoma listerianum, but my reasons for disagreeing with this assumption are elsewhere expressed (Carlisle, 1953). Milne Edwards did not of course describe the course of the sperm duct by whichDiplosoma is distinguished fromDidemnum. In the absence of a description of this diagnostic character we are reduced to a consideration of numerous details of the anatomy of Leptoclinum gelatinosum in order to decide where to place it in the classificatory scheme. When such a point-by-point comparison of shape and curvature of the gut, position of anus, form of atrial and buccal apertures, nature of test, etc., is made, it appears that the one point in which the drawings and descriptions given by Milne Edwards differ betweenL. gelatinosum andDidemnumgelatinosum Mime Edwards (1841) is the presence of a common cloacal system in the former and its absence in the latter. But the presence or absence of a common cloacal system is no longer regarded as a generic distinction (see, for example, van Name, 1945).

This paper is the second of a series dealing with the annual cycle of growth andreproduction in British ascidians; a previous paper (Millar, 1952) dealt with the speciesDiplosoma listerianum (Milne Edwards), Ciona intestinalis (Linnaeus),Ascidiella aspersa (Muller), andBotryllus schlosseri (Pallas)

The present investigation is concerned with the growth, the course of sexual reproduction and establishment of new generations, and the histological changes in the gonad throughout the year, in the ascidianDendrodoa grossularia (family Styelidae).

Samples were examined from two widely separated localities: Fambridge in the River Crouch, Essex; and Farland Point, Isle of Cumbrae, in the Firth of Clyde. The specimens from Essex were dredged from a depth of about 2 m. (below L.W.O.S.T.), and were attached to the empty shells of the European oyster,Ostrea edulis L. and to the shells ofCrepidula fornicata L. The speci-mens from the Firth of Clydewere attached to stones on sheltered parts of the shore. The animals here extended over a zone of the shore from about Chart Datum+ 2.5 ft. (0.76 m.) to about Chart Datum+ 7.5 ft. (2.29 m.): Only in very sheltered positions, such as under large boulders, did Dendrodoa occur in abundance. The two habitats were thus very different in nature, one being sublittoral on the south-east coast of Britain and the other being littoral on the north-west coast. The value of comparisons is limited by the different nature of the conditions to which the sublittoral and the littoral populations were exposed.

The observations on growth in the Clyde extended over most of 1951 and 1952, and nineteen samples were taken.

In previous publications the author (Black, 1948a-c, 1949, 1950a) has reported the seasonal variations in chemical composition that occur in certain of the common Phaeophyceae. In the sublittoral and littoral zones it has been found that a correlation exists between the chemical composition and the depth of immersion of the plant (Black, 1950&, and unpublished work). Differences in composition, particularly during the summer months, also occur in the same species taken at the same time and depth but from different habitats (Black, loc. cit.), and there is also evidence that in the laminarians the stage of development of the plant has a profound influence on the composition. In all the above-mentioned analyses the entire plants have been separated into stipe and frond, dried under controlled conditions, milled, and a well-mixed representative sample of each taken for analysis.

Recently I have reported experiments which have led me to throw doubt on the universal applicability of the theory of the production of a moult-inhibiting hormone by the eyestalks of the decapod Crustacea (Carlisle, 1953). I suggested that the eyestalk moult-inhibiting hormone might be associated with the existence of a definite moulting season. In animals which possessed such a moulting season moultingwould then be inhibited outside this season, but within the season there might well be no such inhibition. The experiments reported here support a modified form of this hypothesis.

If a male dogfish is held in the hand and its belly stroked firmly backwards with the ball of the thumb a fluid can be expressed from the cloaca. In my experience this fluid in a fresh animal invariably contains sperm, whatever the season of the year. After a period of inanition, however, sperm eventually disappears from the cloacal fluid. Such an animal is a convenient test object for gonadotropic activity by a method which closely parallels the toad-pregnancy test of Galli Mainini (1947).

Hake belonging to the genus Merlucdus are large fish often growing to overa metre in length; they are predators, being well streamlined and armed with formidableteeth; they feed pelagically on smaller fish of their own and other species. Of the various species distributed round the ocean basins, the European Hake, M. merlucdus (L.), ranges from Lofoten on the coast of Norway, to Dakar on the African westcoast; it is found most plentifully along the edge of the continental shelf of Western Europe but also extends into the Mediterranean and North Sea, whilestragglers occasionally range as far as Iceland.

The whiting(Gadus merlangus L.) is an abundant food fish in waters to the west and south-west of the Isle of Man. As the stock is at times subject to intensive fishing it seemed desirable to study this species and possibly ascertain the effect of commercial exploitation on the biology of the fish.

Little is known about the development of polynoids. A large number of unidentifiable polynoid trochophores and nectochaetes have been described by Nolte (1936) and others. As Thorson (1946) states, Nolte has done little to clear up the confusion that prevails in this group and his 'numerous figures, all more or less incorrect, and accordingly difficult to recognize, merely serve to further obscure our picture'.

A search of the literature with the aid of Hartman (1951) has so farrevealed only one clearly identifiable member of the family whose early larval stages have been described. Sars (1845a, b), making some of the earliest observations on polychaete life histories, described under the name Polynoe cirrata Fab. the early stages of Harmothoe imbricata (L.). Further studies in some detail on this or a closely allied species were made in turn by Miiller (1851), Mclntosh (1900) and Izuka (1912). The certainty of identification of the parent in this case stemmed from the fact that the early stages, with the exception of those studied by Miiller, were not taken in the plankton but were observed attached to the brooding parent after release from it. In this polynoid the eggs are carried in large masses beneath the elytra, and larvae leave the parent as actively swimming trochophores. This method of carrying the young has also been observed in H. imbricata by Saemundsson (1918) in Greenland and by M. Pettibone (personal communication) in Puget Sound. Desor (1857) quotes the observations of Sars on the brooding habit, and describes the release of trochophores by Polynoe squamata (= Lepidonotus squamatus L. ?) on the New England coast.

The anatomy of some members of the family Calyptraeidae has been adequately described by previous workers (Kleinsteuber, 1913; Giese, 1915; Moritz, 1938), and aconsiderable amount of information has been published on the feeding and the unusual reproductive activities of Crepidula (Orton, 1912; Coe, 1944) Of the anatomy and way of living of the members of those other families of gastropods (Trichotropidae and Capulidae) that Thiele (1929) has unitedwith the calyptraeids in his Stirps Calyptraeacea, much less is known. Orton (1912) and Yonge (1938) have described the feeding mechanism of Capulus ungaricus; and the anatomy of Thyca, a parasitic member of the same family, has been briefly described by Koehler & Vaney (1912). Nothing seems to be known of the anatomy or way of life of members of the Trichotropidae. Yet an investigation of some of these points seems overdue in the lightof Lebour's discovery (1937) that Capulus passes through an echinospira larval stage. This stage does not occur in other members of the Calyptraeacea, although present in two other groups of the mesogastropods, the Lamellariacea and the Cypraeacea. The idea at once presents itself that the capulids may perhaps be more accurately classified as members of one or other of these two groups rather than as members of the Calyptraeacea. The work recorded in the following pages was directed towards answering this question, and would suggest that the original classification is the more correct. The names used are those of Winckworth (1932).

In a recent paper describing the distinguishing characters of British species of Ensis (Holme, 1951), it was concluded that three valid species occur in British waters: E. siliqua (L.), E. arcuatus (Jeffreys) and E. ensis (L.). This paper is an attempt to analyse the ecological factors controlling the distribution of these species, particular attention being paid to the effect of soil grade.

In a previous paper some effects of anisosmotic and unbalanced salt solutions ontheluminescent responses of Chaetopterus variopedatus have been described (Nicol, 1952). Similar experiments have been carried out on polynoid elytra, andthe results are described elsewhere in this Journal, together with a brief review ofthe relevant scientific literature (Nicol, 1954b). The present experimentswere undertaken to investigate the effects of single salts in physiological concentrations, balanced by the addition of some inert substance, and to explain the possible mechanism of stimulation by hypo-osmotic solutions.

When stimulated in some suitable manner Chaetopterus secretes a luminescent material into the surrounding sea water. The luminescent secretion is discharged fromglands which are widely dispersed over the surface of the animal; the most conspicuous are two glandular patches on the dorsal surface of segment XII. Secretory materialis forced out of the cells by some contractile process; discharge is not merely theresult of secretion pressure. Under repetitive stimulation the intensity of the luminescent response decreases owing to the intervention of fatigue. Fatigue has been interpreted as a gradual exhaustion of luminescent material in the glandular cells (Nicol, 1952b,c).The present investigation seeks to analyse the onset and progress of fatigue in greater detail.

The main picture of the zonation of life between tide marks on British shores has been added to by a good deal of recent work, such as that of Colman (1932) and Evans (1947) at Plymouth, and the regional studies by Stephenson & Stephenson (1949). Of the more restricted special habitats within the tidal area there have been fewer accounts, though Colman (1940) has made a detailed survey of the faunas inhabiting intertidal seaweeds, which was later followed by Wieser (1952). Most recently there has appeared a paper by Glynne-Williams & Hobart (1952), working at Anglesey, which for the first time analysed clearly the composition and food relations of the restricted fauna living in crevices in this habitat. This part of the tidal zone forms an interesting meeting place of two faunal elements, those intertidal animals of terrestrial origin and those which are truly marine. In the summer of 1950 and 1951 the present writer had made a similar study in the Plymouth area, at Wembury and some other localities. The work was begun as part of an ecological study of the two marine pulmonates Leucophytia bidentata and Otina otis, and was later extended to take account of the other animals hidden in crevices and those living on the exposed rock surface throughout the upper half of the tidal zone.

Some preliminary observations on luminescence in polynoid worms have been presented in a previous paper (Nicol, 1953). These animals produce light in scales (elytra) which cover the dorsal surface of the body. The source of the light lies in a layer of unicellular epithelium on the lower surface of the scale. Histologically, this tissue consists of columnar cells (photocytes), characterized by the presence of coarse eosinophilic granules in the cytoplasm. The nervous supply of the elytrum derives from a nerve trunk which ascends the stalk or elytrophore and proceeds to a ganglion in the centre of the scale. From this ganglion nerves radiate peripherally and proceed to the photocytes, and to sensory receptors on the dorsal surface and at the margin of the scale (Bonhomme, 1942).

For routine sampling of the infauna of the sea bottom an apparatus is required which is simple, easily handled, and which can give samples of consistent volume from different types of bottom and in varying weather conditions.

The Petersen sampler and its modification, the van Veen, are simple and easily handled and give reasonably consistent samples from some types of soil. But on hard ground they are less satisfactory, and in rough weather they tend either to land unevenly on the bottom, thereby taking smaller samples of variable volume, or to release in mid-water with the rolling of the ship, so that no sample is taken.

Little is known of the biochemistry of diatoms, although many workers have reported growth experiments with the unicellular algae of the marine phyto-plankton. Experiments have often been performed without due regard for the appropriate control of physical and chemical conditions. Many reports contain only incomplete data of the growth under a given set of conditions, and it is often impossible to say whether the effects recorded are upon the growth rate, the total crop, or both. Other studies have been reported which included the addition of organic matter to cultures which were only uni-algal and not bacteria-free. At the present time even the mere maintenance of stock cultures of the marine unicellular algae is perforce an empirical matter. Results in replicate cultures often show gross differences in growth that are apparent on inspection by eye alone, and insufficient information is available regarding the nature of these variations in growth to allow the rational development of improved culture media. Due therefore to a lack of suitable techniques, most of the results available are difficult, if not impossible, to interpret in terms of the biochemical activities of the algae.