Opisthobranchs are mostly unsuitable animals for detailed ecological work since it is unusual to come across an adequate population for quantitative analysis. This difficulty is reflected in the generalized surveys that may be found described in the literature and which deal with a large number of species, each in little detail (Garstang, 1889; Swennen, 1961; Miller, 1961; Thompson, 1964; Schmekel, 1968). Very few detailed works on a single species are found of the kind published by Thompson (1966) on Archidoris pseudoargus (Rapp). Most often ecological notes are available as a by-product of works involved chiefly with anatomy and taxonomy. The result is that, in the absence of facts, hypotheses are formed to cover portions of the life histories of nudibranchs about which little is known. The problematical migrations attributed to nudibranchs is a case in point and, as the summaries of Costello (1938) and Miller (1961) show, there would appear to be several ways of interpreting the scant data.

The growth of certain unicellular marine algae has been shown to occur in culture solutions whose total ionic content and chemical composition departs markedly from that of natural sea water. In fact, some of these algae apparently grow more rapidly in half-strength sea water media than in a medium of salinity equal to 35‰. This ability, on the part of the algae, to grow at widely different salinities suggests that the algal cells are able to maintain an internal ionic composition despite wide variation in the external composition of the surrounding culture medium in which they are growing. Droop (1958) has shown that the major cations present in sea water can be varied within wide limits and it was decided to concentrate on the cations, sodium, potassium, calcium and magnesium. A series of analyses of Phaeodactylum tricornutum has been carried out to determine the concentrations of the four cations present in the cells and also to determine whether these concentrations vary during the growth of cells in culture over a period of time. In addition the analyses have been carried out on cells which have been grown at two different salinities, to compare internal cellular concentrations at different salinity levels of the media.

During the autumn of 1965 a detailed study was carried out by members of the National Institute of Oceanography and Scripps Institution of Oceanography into the vertical distribution of the micronekton, plankton and sonic scattering layers in the upper 1000 m at a position off Fuerteventura in the Canary Islands. This is one of a number of similar papers by various authors on the vertical distribution of the animal groups sampled (Angel, 1969; Clarke, 1969). A background to the investigation, including the hydrology of the area studied, has been given in an introductory paper by Currie, Boden & Kampa (1969).

Jørgensen (1944) showed that young specimens of the siliceous freshwater sponge Spongilla lacustris L. obtained their skeletal silica from the water and demonstrated that, under experimental conditions, a relationship existed between the size of the microscleric spicules produced and the concentration of dissolved silicate in the culture medium. The thickness of the microscleres increased with increasing concentration of dissolved silicate in the medium but no changes were detected in the lengths of the microscleres or in the size of the megascleres. Prior to this report Jewell (1935) showed that specimens of 5. lacustris with normal spiculation were rarely found in natural waters with a silicate content below 0.005 to 0.01 mm Si02. Hartman (1958) suggested that the greater thickness of siliceous spicules found in specimens of Haliclona caniculata Hartman collected in winter from New England shores, compared with spicules from summer-collected specimens, might reflect the increased concentration of dissolved silicate in the sea water during the winter months. Similar effects have been demonstrated experimentally in calcareous sponges: Maas (1906) showed that calcareous sponge larvae reared in calcium-free water produced no mineral spicules but organic ‘spiculoids’ of similar form. A relationship between spicule size and environmental silicate has not, in the past, been conclusively demonstrated for any siliceous sponge in field conditions.

When electro-osmosis is observed through a substance (or tissue) certain inferences can be made about the fine structure of the substance. These include the presence of a zeta potential whose sign is the same as that of the electrode towards which water moves, and the presence of interstices or channels large enough to allow ions to move through them and to sweep along more water molecules than those carried as hydration shells. Channels too large may permit both positive and negative ions to move or at least allow a counter flow of water to reduce the net (observable) movement of water molecules.

Spontaneous rhythmic activity in the lugworm Arenicola marina (L.) is believed to be under control of a pacemaker located in the ventral nerve cord and oesophageal plexus (Wells, 1937). Since the rhythmic component which often dominates the spontaneous behaviour of polychaete worms consists of movements resulting in irrigation of the tube or burrow, and thus ventilation of respiratory surfaces, pacemaker control of the rhythm differs strikingly from reflex control of ventilation in other animals.

Only three of the twenty species at present ascribed to the genus Mysidopsis have been recorded around the coasts of Britain; these are M. gibbosa G. O. Sars, M. didelphys Norman and M. angusta G. O. Sars. The latter species is rare and has never been caught in large numbers. Large catches of M. gibbosa are made in certain sandy bays in the Firth of Clyde and the species is quite common in Gaineamh Smuagh, a sandy bay in Loch Ewe, Wester Ross (Mauchline, 1965 a). The largest species, M. didelphys, occurs at greater depths than the other two and, like M. gibbosa, is often common in certain areas, especially in the deep troughs of the Firth of Clyde and in some of the west coast lochs of Scotland, for example the upper part of Loch Etive.

SOND Cruise 1965 aboard the R.R.S. ‘Discovery’ afforded the opportunity for short-term estimation of the penetration of daylight at midday into three regions of the eastern North Atlantic, evaluation of the fluctuations in the character of noonday light at depth in a restricted area over a 2-month period, and a determination of the penetration of moonlight in this area at the full of the moon.

One of the puzzling features of polychaetes and some other animals is the tendency for epidermal mucus cells to become incorporated into the central nervous system (Clark, 1966). In a number of species of Nephtys an extensive prostomial mucus gland system has come into close association with the supraoesophageal ganglion of which it sometimes forms two enormous posterior lobes (Clark, 1955, 1958). Cells which are comparable to, if not homologous with, those in Nephtys are even more completely incorporated into the supraoesophageal ganglion of nereids (Bobin & Durchon, 1953; Durchon & Frezal, 1955; Hauenschild & Fischer, 1962; Herlant-Meewis & Van Damme, 1962) and glycerids (Simpson, 1959), though, unlike the situation in nephtyids, the connexion between these cells and the exterior is tenuous or even problematical in nereids and glycerids. In Pisione, superficial gland cells near the median ocelli of the trochophore larva are incorporated into the supraoesophageal ganglion at metamorphosis and form two well-defined glandular masses near the posterior eyes in the adult, losing their ducts to the exterior in the process, but retaining the appearance of gland cells (Åkesson, 1961).

The secretion of mucus has been most intensively studied in goblet cells and mucous salivary gland cells from mammals, particularly laboratory rodents. It was therefore thought desirable to characterize mucous cells from the gut of Ciona intestinalis (L.), in which mucus has an important role in food capture, the formation of a food chain, the protection of the gut lining from physical and chemical abrasion and the formation of faeces. The alimentary canal of Ciona is composed of five regions: (I) a perforated pharynx, (II) a short tapering oesophagus, (III) an ovoid ridged stomach, (IV) an intestine and (V) a rectum. Previous authors (Roule, 1884; Yonge, 1925; Van Weel, 1940; Millar, 1953; Fouque, 1954) have described the preponderance of mucus-secreting cells which occur in the oesophagus, intestine and rectum. It is these three regions that have now been studied in more detail, with the use of histochemical and electron-microscopic techniques.

Knowledge of the distribution of molybdenum in sea water is needed for an understanding of the behaviour of the element in the geochemical cycle of weathering and sedimentation and for the assessment, in relation to environmental levels, of its possible utilization by marine organisms. The principal measurements of molybdenum in sea water are summarized in Table 1; the results of earlier investigations (Ernst & Hoermann, 1936; Bardet, Tchakirian & Lagrange, 1938; Noddack & Noddack, 1940) are excluded from this summary as later work suggests that they were inaccurate. The summary indicates that molybdenum is a comparatively uniformly distributed trace element in sea water with a concentration usually in the range of 9–13 µg/l. Except for waters directly affected by continental drainage or other localized influences, the only values appreciably below this range appear to be those reported by the early workers cited above, by Zhavoronkina (1960) for a single sample from the Atlantic, and by Brooks (1965) for waters off New Zealand.

A pure-cone retina has been reported in the larval stages of teleosts from three families, viz. the salmon Oncorhynchus spp. by Ali (1959), the herring Clupea harengus by Blaxter & Jones (1967) and plaice Pleuronectes platessa by Blaxter (1968 a). There is also an absence of any retinomotor responses (movement of retinal masking pigment and changes in the relative positions of the visual cells) until the rods develop, which is usually at metamorphosis where this is clear-cut. Most adult teleosts are known to have a duplex retina.

There is now much information from field observations and laboratory experiments on pollution by oil and oil-spill removers (‘detergents’) in inshore waters and littoral habitats in SW England following the wreck of the Torrey Canyon on the Seven Stones Reef. Field observations with particular reference to plant life were reported by O' Sullivan & Richardson (1967), Spooner (1967), Nelson-Smith (1967), and Bellamy et al. (1967). A detailed survey of the biological effects of the disaster has been published (Smith, 1968). Further data dealing with littoral and sublittoral algae have been reported by Ranwell (1968), Bellamy & Whittick (1968), Boney (1968) and Nelson-Smith (1968). It has been shown from both field observations and laboratory experiments that the larger fucoid algae were more tolerant of both the oil and the oil-spill removers than the smaller algae in the region of high-water mark.

The genus Bathyporeia has featured in many reports on the ecology of sandy beaches, yet little is known of the annual reproductive cycles of the species in British waters. Watkin (1938,1939a, b, 1941, 1942) has studied the taxonomy and aspects of the ecology of the genus, and more recently Salvat (1967) has described the annual reproductive cycle of B. pilosa Lindstrom, B. pelagica (Bate), B. sarsi Watkin and B. guilliamsonia (Bate) on the west coast of France. The present report is the result of an investigation into the vertical distribution and annual reproductive patterns of B. pilosa and B. pelagica on a sandy beach at Ynyslas, Cardiganshire. Whilst enabling comparisons to be made with Salvat's data, this study also forms the basis for an investigation into the ecophysiological complex of B. pilosa and B. pelagica.

Suspended organic matter in the oceans has been studied by many authors. In a review of the subject Parsons (1963) states that the occurrence of detritus particles in the oceans seems to be a universal characteristic of sea water. The greatest concentrations of suspended organic matter are to be found in turbulent inshore water masses.

The view that bivalve molluscs are ideally adapted to fulfilling a mode of life in which the processes of feeding and digestion are continuous has long been accepted by most zoologists. An increasing amount of evidence, how ever, is being put forward to suggest that the opposite is true, that is, that bivalves are discontinuous in their feeding and digestive habits.

In 1801 Vaucher discovered the oogonia of Vaucheria—or Ectosperma as he called it—but he described the antheridia in a very incomplete way without seeing the spermatozoids (Vaucher, 1801, 1803). These were first observed some fifty years later by Pringsheim (1855), who also saw fertilization, one of the first observations on fertilization to be made in the lower plants.

In a recent study (Butler, Corner & Marshall, 1969) it was found that the excretion of nitrogen and phosphorus in soluble form by Calanus finmarchicus caught at Garroch Head in the Clyde sea-area was significantly higher in spring when plant food was plentiful, than in autumn when plant food was in relatively short supply. The present survey has extended this earlier study to include more detailed data at all times of the year, particular attention being paid to the spring diatom increase of 1969 when plant food in the sea near Garroch Head rose above the level which Beklemishev (1962) regards as inducing superfluous feeding, a wasteful process partially involving the inefficient assimilation of foodstuffs (see ‘Discussion’, p. 549).