The Scaphopoda or tusk-shells are the smallest and most uniform class of molluscs. They burrow in sand of medium to coarse shelly grade, and specialize on a diet of hard-shelled microbenthos, particularly Foraminifera. Dentalium entalis L. is the commonest West European species, and may become locally dominant. Le Danois (1948) has described a ‘Dentalietum’ in deeper water sandy ground at about 100 fathoms in the southern Celtic Sea. Stephen (1933) discusses the distribution of D. entalis in the northern North Sea, where it is largely restricted to the ‘Offshore zone’, the southern limit being marked by the 60 m line. Low salinity is probably responsible for its absence from the southern North Sea; and in general it seems limited more by hydrographic conditions than by the relative abundance of foraminiferan food. For example, in Stephen's Thyasira+ Foraminifera Zone, it is no more than sparsely present. Holme (1953) finds Dentalium entalis rare or absent near Plymouth, though it was relatively common at the Eddystone Grounds at the end of last century (Allen, 1899). It has today receded to the mouth of the Channel, in coarse deposits resulting from fairly strong scour, and Holme suspects it to be one of the list of species sensitive to recent hydrographic changes in the area.

For the living material used in this study I am greatly indebted to Mr N. A. Holme, who collected it in deeper water in the Celtic Sea on a 1953 cruise of the R.R.S. ‘Discovery II’. With it were collected Chlamys opercularis, Caryophyllia and in places Astropecten irregularis; there were also many of the tusk-shaped serpulid tube worm Ditrupa arietina which as I found can impose a neat deception on the uncritical hunter for scaphopods.

No account exists of the mechanism of food collection of nudibranch larvae, and, in fact, it has been considered unlikely that feeding does take place in these forms. Thorson (1946, p. 275) states ‘Nudibranch larvae will normally take no—or only little—food from the plankton’.

Among the parasites of the branchial chamber of the flatfishes of the Eastern North Atlantic, those belonging to the genus Acanthochondria (fam. Chondracanthidae, tribe Cyclopiformes) occupy a conspicuous place. Both their relatively large size and their abundance, render them easily noticeable even to a casual observer, in spite of the protective nature of their environment. It is a reflexion on the state of our knowledge of marine parasites that, not withstanding their accessibility, very little is known about the animals of this genus.

The genus Acanthochondria was erected by Oakley (Leigh-Sharpe and Oakley, 1927) for the chondracanthids, which until then were included in Chondracanthus Delaroche, 1811, and which differed from the other members of that genus in the absence of the cephalic barbs and the dorsal and ventral processes. They were also characteristic in their preference for the flatfish hosts.

In spite of the keen interest evinced in the taxonomy of the parasitic copepods, there is little information on their metabolic rate, though the respiration of free-living forms has been studied by such workers as Marshall & Orr (1955, 1957), Clarke & Bonnett (1939), Zeuthen (1947), Raymont & Gauld (1951), Gauld & Raymont (1953) and Conover (1956). Since the rate of oxygen consumption is a reflexion of the metabolic rate of an animal, it was felt that a study of the rate of oxygen consumption of a copepod parasite would be of interest. Chondracanthus zei De la Roche, 1811, is easily available and large.

Biebl (1939a, b) has found that algae from various ecological groups show marked differences in their resistance to changes in the temperature of the surrounding sea water. He regards this temperature effect as an important factor influencing the distribution of different intertidal algae and points out that a change of only 2° C may prove critical with certain species. One of us (A.D.B.) has studied the resistance of sporelings of various common inter-tidal red algae to changes in environmental temperature and has obtained results similar to those of Biebl.

The species with which this paper deals was originally included by Linne in the genus Solen and was there retained to be included under that name in the magnificently illustrated account of this genus by Deshayes (1845–48). It was later placed in a new genus Ceratisolen by Forbes & Hanley (1853) who considered that it formed ‘the connecting link between the Solenidae and Solecurtidae’. This procedure was followed by Jeffreys (1865). More recently the Solecurtidae were shown by Graham (1934b) having ‘regard to such features as shape, presence of a cruciform muscle and the structure of the foot, siphons, adductor and pedal muscles, supra-axial extension of the outer demibranch, palps, and style-sac and intestine’, to belong to the Tellinacea, a view fully supported by this author (Yonge, 1949). Assigned later to the genus Pharus which has priority over Ceratisolen, this ‘connecting link’ of Forbes & Hanley continued to be associated with the Solenacea by Thiele (1935) in his great systematic account of the Mollusca.

The importance of Meganyctiphanes norvegica (M. Sars) as a source of vitamin A for its predators has been demonstrated by Fisher, Kon & Thompson (1955). Basing their conclusions on the observations of Macdonald (1927) on the feeding of M. norvegica in Loch Fyne, Fisher, Kon & Thompson (1954) and Kon (1954) suggested a possible scheme of accumulation of vitamin A in the animal. They also made cursory examinations of the stomach contents from animals caught in the same area and their findings appeared to agree fairly well with those of Macdonald, except that from his results he concluded that phytoplankton was a major item in the diet. This conclusion has been disputed by Einarsson (1945) who called for more detailed investigation of fresh material in order to obtain a clearer picture of the feeding of north Atlantic euphausiids. Such information would be of great value in the study of the vitamin A chain in the plankton. We have, therefore, examined the stomach contents of M. norvegica over nearly two years to try to detect every type of food that might be eaten. In addition to our own survey, Dr J. Mauchline (1959) of the Marine Station, Millport, made a more intensive study of the food in relation to the diurnal migrations in July and November.

The redistribution of sediments by tidal streams has been demonstrated in a number of ways in the seas around Britain. For example, the numerous banks in the North Sea are elongated parallel to the streams, while the depth and position of certain channels are subject to such important changes in position that re-surveys have to be made each year or so (Robinson, 1956). In the same region the streams, reaching about a knot or more at the surface, have wrought a large area of sand floor into ridges normal to their path. Off the Dutch coast the grade of the sand (Jarke, 1956) decreases in their inferred direction of advance (Stride & Cartwright, 1958). Similar relief is found even at 90 fathoms near the edge of the continental shelf, at the western approaches to the English Channel (Cartwright & Stride, 1958). Pratje (1950) has shown that the occurrence and grade of loose sediment on the floor of the Channel as a whole is directly related to the velocity of the streams overhead.

The marine plankton flagellate hitherto known as Chromulina pusilla Butcher is one of the smallest of algal cells, being of bacterial dimensions (1–1.5µ, Butcher, 1952). For this reason it had seemed of interest to investigate its structure with the electron microscope as part of a general programme on ciliated cells in plants which has been in progress for some years. It soon became apparent, however, that there were more points of importance than had been expected at the outset. In particular the anatomical findings showed that the formal taxonomic description based on the light microscope was not only incomplete (an unavoidable consequence of the very small size), but that, as a further consequence of these physical limitations, it contained some rather fundamental misconceptions regarding the taxonomic position of the organism. By the kindness of correspondents and collaborators it was fortunately possible at once to follow up the anatomical evidence biochemically, and the combined data make the conclusion unavoidable that this organism is not a member of the Chrysophyceae (to which group the genus Chromulina properly belongs) but that its affinities lie in or near the Chlorophyceae. This naturally raises some difficult nomenclatural questions which cannot all be immediately resolved. The anatomical facts for this particular species are not, however, in themselves dependent on nomenclature, and since this organism is not merely an electron microscopical curiosity but is also exceedingly abundant in coastal waters near the British Isles, it is perhaps of some value to students of plankton that they should be made available.

Although it has been stated (Thomson, 1927, p. 234; Elliott, 1953, p. 264) that the descending branches of the loop in dallinids, so far as is known, grow from the crura only, yet figures supporting this statement have not so far been published, not even by Beecher (1895) who described the very early stages of lophophore and loop in Dallinella (=Terebratalia) obsoleta (Dall). Tiny specimens of Macandrevia cranium dredged by R. V. ‘Sarsia’ have now made it possible for such figures to be published. It is a point of some importance as it is one of the characters given by Thomson (1927, p. 234) as distinguishing the Dallininae from the Mühlfeldtiinae (= Megerliinae Muir-Wood, 1955) and the Magellaniinae (= Terebratellinae, see Muir-Wood, 1955), for in the two latter groups the descending branches of the loop grow from both crura and septum to unite in the middle. At the time Thomson was writing, young growth stages of the loop of a member of the Laqueinae were not known. Since then, Konjoukova (1948, 1957) has studied the development of Laqueus californicus—which she placed in the Dallininae—and according to her the descending branches on reaching the septum join with it. She does not, however, figure any intermediate stages between absence of descending branches and complete ones. In 1941 Laqueinae was raised to family rank by Yabe and Hatai (see Muir-Wood, 1955, p. 93).

Eye-stalk removal in certain species of Brachyura and Astacura has almost invariably led to the initiation of proecdysis. In other decapod crustaceans, however, there have been significant variations in the results of this operation. Thus Travis (1951) found that eye-stalk ablation had no effect on the duration of the moult cycle in Panulirus argus. And in the Natantia, even in a single species, quite different results have been reported. Drach (1944) found that eye-stalk removal in Palaemon (=Leander) serratus (Pennant) led, as in crabs, to the initiation of proecdysis and to accelerated moulting. In ignorance of this work I repeated some of the same experiments and found that eye-stalk removal in P. serratus led to slower moulting (Carlisle, 1953 a)— a result quite opposite to that of Drach. Scheer & Scheer (1954) confirm my results in the same species.

In order to provide more factual information on the effect of Echinus predation (Forster, 1958), further diving observations have been made during 1958. A rocky areajust west of the Tinker Shoal was explored by chance and a population of Echinus discovered. As this area is much more readily accessible than Stoke Point rock, where most of the diving has been carried out, it was possible to establish a marker buoy and make a number of dives on exactly the same position. In the course of these dives I have attempted to measure the numerical density of the urchins and the rate of their browsing on the rock surface. Later Echinus ‘counts’ were made at many other positions near Plymouth (Text-fig. 1).

The affinities, structure and distribution of species of the genus Tetraplatia Busch, 1851 have been discussed recently by Hand (1955), Beyer (1955) and Rees & White (1957 a), but ever since these curious bipyramidal medusae (without a typical medusan bell, marginal tentacles, or gastrovascular canals) were described by Busch they have provided much interest for the systematise There is unanimous agreement that the clearly discernible nematocyst tracts, and the body wall of ectoderm and endoderm separated by a thick, well-defined mesogloea, place them within the Cnidaria as known at present. Tetraplatia is usually regarded as the only member of the hydrozoan order Pteromedusae, but Komai (1939) strongly advocates scyphozoan rather than hydrozoan affinities. The purpose of this paper, however, is not to discuss the broad relationships of the Pteromedusae, but to give further evidence that Tetraplatia chuni Carlgren, 1909 is a good species. (The structure and affinities of Tetraplatia will be discussed in another paper.)

Anatomical and histological details are here given of two organ systems, which, my experiments lead me to believe, may secrete hormones concerned in the sex reversal that overtakes all male Pandalus borealis Kroyer. The descriptions eschew any attempt at detailed cytology, and refer exclusively to prawns taken from the population of Gullmarf jord in south-west Sweden. There is reason to believe that, as with Palaemon (= Leander) serratus (cf. Carlisle, 1955), different populations may vary widely in the detailed topography of the endocrine organs, as well as in appearance, life history and growth rate (cf. Horsted & Smidt, 1956).

As a result of work by Pirlot (1933), Newell (1948), Smidt (1951) and Duncan (1953) it has become accepted that on European coasts the lugworm has a restricted breeding season occurring only in the autumn. Previously, several workers had stated that this species also spawns in the spring. Kyle (1896) reported that at St Andrews spawning took place between January and March and again between July and September. Similarly, Gamble and Ashworth (1898) and Ashworth (1904) found that on the Lancashire coast the laminarian variety spawned in the spring, although the littoral variety spawned during late summer.

Relatively little is known of the exact role of the thyroid gland in teleosts. Although the results of a few studies have suggested that the thyroid influences respiratory metabolism, as in the higher vertebrates, a greater number of experiments have failed to show that either treatment of fish with thyroid hormones or inactivation of the gland produces any significant effect upon the oxygen consumption of the fish. Thyroid activity has been linked with reproduction in some fish, although there is little evidence to show that the relation-ship is more than coincidental. The thyroid has also been connected with osmoregulation, but reviewing this work Pickford (1957) concludes that the relation with osmoregulation is only a secondary or collateral one. Recently Hoar (1953, 1955) has suggested that the thyroid may control the migratory response of fish. However, in the migratory species which have been studied in detail, the salmon, Salmo salar L. and Onchorhynchus spp. and the eel, Anguilla vulgaris, changes in the salinity of the environment during their migrations were complicating factors since salinity changes alone have been shown to stimulate thyroid activity in non-migratory fish (Olivereau, 1954).

Describing the migrations and movements of the cod, Gadus callarias L., in the Barents Sea, Trout (1957) suggested that the immature fish carry out a false spawning migration. ‘The pattern of migration of the immatures is basically similar to that of the matures…with increasing age, the immatures’ southerly winter migration approached in length that of the mature cod, as if, in the years immediately prior to maturity they were making a “dummy run” towards the spawning ground.' The seasonal migrations of both the adult and immature cod have been related to changes in the activity of the thyroid gland in this fish (Woodhead, 1959). During the spring of 1956 and 1957, collections of thyroid glands from immature cod were made at stations from Bear Island to the Norwegian coast. It was hoped that a study of these glands might demonstrate further the relationship of the activity of the thyroid gland to the migration of the fish.

Sea surface temperatures have been taken daily at Keppel Pier, Millport (55° 44‘ 55“ N. lat.; 4° 54’ 20” W. long.), for the past 10 years (1949–58), the data being included in returns to the Meteorological Office. The records are not given in their standard publication and they are, therefore, presented here to supplement those of Cooper (1958) for inshore waters at Plymouth some 400 miles farther to the south. For some years the samples were drawn in a specially constructed container fitted with a Fahrenheit thermometer which was read to the nearest whole degree; more recently the bucket method has been used, and a centigrade thermometer graduated in degrees and read to an estimated tenth of a degree. The two methods were checked against each other before the change was made and the results found to be consistent. All readings were taken at 09.00 h G.M.T., irrespective of the state of the tide. The results are shown in Table 1.