The hydroid of the Anthomedusa Bougainvillia britannica Forbes has not been known with certainty, though its identity with B. flavida Hartlaub has appeared probable.

From colonies found on Aporrhais pespelecani in the Firth of Clyde medusae of B. britannica have been reared. A description and figures of the hydroid and the young stages of the medusa are given.

Bougainvillia flavida Hartlaub and B. linearis (Alder) are junior synonyms of B. britannica Forbes.

Tubifex costatus is a marine euryhaline species of tubificid, commonly found in brackish water. It is common in estuaries, where it colonizes a wide variety of substrata.

The species breeds sexually once a year in early summer, and it is likely that it takes 2 years to reach maturity, and after breeding it dies.

There is only one likely predator, Nereis diversicolor, and the population of T. costatus seems to be kept at a very constant level.

Ability to tolerate low salinities has been compared in homozygous adult females of the trifasciata and violacea forms of the polymorphic copepod Tisbe reticulata from Chioggia (lagoon of Venice). Both forms appear to be equally capable of tolerating sea-water concentrations of between 100 and 33 %. Further comparison with the trifasciata form of T. reticulata from Plymouth and with three different geographical populations of Tisbe furcata has shown that these copepods are rather less tolerant.

A study of ionic regulation using the isotopes 22Na, 42K and 137Cs has shown that in diluted sea water T. reticulata does not control the body Na concentration but does control the K concentration. Exchange rates for 42K and 137Cs are higher in the violacea than in the trifasciata forms of T. reticulata from Chioggia and the difference may have an adaptive nature although its significance is not clear. With regard to 42K, the difference between the two polymorphic forms from the same population of T. reticulata is greater than that between the three different geographical populations of T. furcata. This serves to add more emphasis to the fact that colour polymorphism in T. reticulata can be associated with other processes.

After transplantation and acclimatization of populations of the barnacle Balanus balanoides from the coast of New England to the Menai Straits, differences in breeding behaviour persisted over a period of from 4 to 18 months. The two populations are believed to belong to distinct physiological races.

The New England populations fertilized 1½–3 weeks in advance of adjacent British populations.

Embryonic development in the post-cleavage stages of the New England population proceeded in vitro at about twice the rate of the development of the British population, under identical conditions.

The volume of the eggs of the New England population was 1.3–1.6 times as great as the volume of the eggs of the British specimens.

Both populations, when growing in British waters, liberated their nauplii in March at a time which coincided with the beginning of the vernal plankton increase in the locality. The embryos of the American population had therefore remained in the mantle space for a much longer period than had those of the British specimens and for a longer period than that reported for New England populations in their native habitat.

In B. balanoides the time of fertilization and rate of development may be genetically adapted in each general locality so that the embryos reach full term before the plankton increase is due. The actual time of liberation is then mediated by the hatching substance in response to prevailing food conditions.

If the B. balanoides population of the Western Atlantic area as a whole belongs to a physiological race distinct from that of the Eastern Atlantic, and responding differently to temperature levels at the breeding season, there is no reason to expect any close correlation in respect of environmental conditions between the southern limits of the species in Europe and in America.

The seasonal fluctuation in numbers of C. tentaculata was investigated from December 1959 until February 1962. The lowest numbers were recorded in April followed by a rapid increase in numbers during May. The magnitude of the increase varied from year to year, as also did the number of peaks that occurred during the summer months.

The worm was shown to have an extended breeding season from the end of March to September during which several spawning ‘bursts’ took place. Experiments suggest that some spawning may occur when the mudflat is inundated by the rising tide, although spawning was not observed in the field.

The population of C. tentaculata exhibited an annual cycle of growth which was influenced by the seasonal variation in temperature. Laboratory observations suggest that a temperature of about 20° C is optimal for the growth of young worms. The growth rate (8 mm/year) is slow compared with that of other polychaetes.

It is tentatively concluded from the field mortality data that between 10 and 16 % of animals survive to an age at which they are sexually mature; between 6 and 8 % of each generation reach an age of 15 months. Causes of mortality in the population are briefly discussed.

Some ecological data concerning the Plymouth species of Leucosolenia are given, together with a discussion of the speciation of the British Leucosolenia.

Oscular tubes of L. variabilis have been photomicrographed at intervals, usually of 1 or more days. It was found that the choanoderm boundary at the proximal end of the oscular rim may advance, remain stationary, or recede in relation to the distal edge of the tube, according to the conditions. It may also move in either direction in relation to the spicules in its vicinity, regardless of how it is moving with respect to the oscular edge. The evidence indicates that the choanoderm is mobile on the inner surface of the tube and that the level of the choanoderm boundary is influenced by the surface area available and by the rate of multiplication of the choanocytes. The former depends upon the degree of contraction or expansion of the tube and the size and number of pores.

The arrangement of the choanocytes can alter within a few minutes. The cells, however, tend to cohere; their outlines near the base are polygonal and there is a thin hyaline layer separating the surfaces of adjacent choanocytes.

The beating of the flagella is uniplanar, the plane being perpendicular to the wall. The frequency of the beat varies from one choanocyte to another, as does also the orientation of the plane of beating. The latter does not alter when a current of water is drawn across the choanoderm. Excision of an oscular tube results in water flowing out at both ends as soon as the cut has been opened.

Assays and mixed culture experiments prove that the supply of chelating substances is frequently the most crucial aspect of phytoplankton nutrition in sea water. Experimental results, theoretical considerations and tentative calculations show that this supply is controlled by the stability of the trace metal chelates and in the sea may be mediated by certain unknown minor components of the dissolved organic matter.

The results of Parts I and II are considered together and show how seawater quality is closely related to the chelation of trace metals, mainly iron, and various other factors previously listed in the summary to Part I.

Nerves known to supply the anterior part of the vena cava in Cephalopoda have been found to belong to a special system for which the term ‘neurosecretory system of the vena cava’ (NSV system for short) is proposed. In Eledone cirrosa this system consists of neurons whose cell bodies are aggregated: (a) in the visceral lobe in a layer termed the NSV layer; (b) in the ganglionic trunks continuous with this layer and associated with nerves arising from the visceral lobe—there is on each side a ‘lateral NSV trunk’ accompanying the nervus infundibuli posterior, and a ‘medial NSV trunk’ accompanying the nervus visceralis. Each of these trunks in its further course separates from its nerve and runs far in the caudal direction diminishing in thickness and giving off sideshoots of irregular shape which end blindly in the loose connective tissue and show no connexions with any organ.

The NSV layer and trunks consist of unipolar nerve cells of small size and uniform appearance. Their very thin axons unite in bundles which form nerves running to the vena cava. The total number of neurons of the NSV system, approximately estimated, must be over two millions. The disposition of the elements of this system is peculiar in that the axons of the cells situated in the caudal prolongations of the ganglionic trunks must run far rostralwards until they reach the nerves to which they contribute.

The nerves entering the vein penetrate through its muscle coat and form a network under the endothelial lining of the vein; this continuous neuropile layer extends from the anterior end of the vein to the entrance of the vena hepatica; all this part of the vein has on its inside longitudinal ridges formed by the uneven thickness of the neuropile layer.

The characteristics of the genus Pelagia are discussed.

It is concluded that two good species, P. noctiluca (Forskål) and P. flaveola Eschscholtz, are already described.

A third species P. colorata n.sp. has been erected for the medusa recorded from time to time from the coast of California which has been reported previously as P. noctiluca var. panopyra.

The growth in culture of Laminaria saccharina (L.) Lamour. and a species from Nova Scotia, tentatively identified as L. agardhii Kjellm., has been compared. Several characters, normally used for specific distinction within the genus Laminaria, have been shown to be modified by environmental conditions. These all concern the lamina and include the following: general morphology and texture, the shape of the base, the anatomical construction and the presence or absence of mucilage canals.

The question of the identity of L. agardhii from eastern and western Atlantic coasts is discussed.

The general histology of the integument of the ophiuroid Ophiocomina nigra is outlined. Two types of integumentary mucous glands are described in detail for the first time. The first is a multicellular gland, the basal end of which is located deep within the calcareous layer of the integument. The source of the secretion is a variable number of nuclei embedded in a common cytoplasmic mass filled with fine basiphil granules. These cells contributed their secretion to a duct which pursues a tortuous course through the integument. The ducts frequently branch and anastomose so that any one exit pore may extrude mucin derived from a number of separate, polynuclear sources. The structure so formed is, thus, a massive, multicellular gland. Histochemical studies demonstrate that the mucin is a highly sulphated acid mucopolysaccharide. The second type of mucus-secreting unit is a unicellular gland usually located superficially in the calcareous layer or sometimes restricted to the epidermis and distributed universally over the body. The secretion product of these cells is shown histochemically to be a simple acid mucopolysaccharide. The mucin secreted by the tube-foot glands is demonstrated also to be a highly sulphated acid mucopolysaccharide.

The function of these secretions has been investigated to some extent. The massive glands secrete only under conditions of alarm and it is suggested that this mucus serves as a defence against predation. The unicellular glands secrete in a periodic fashion correlated with the act of feeding. This secretion is probably utilized in a suspension-feeding mechanism.

An apparatus and experimental method for the investigation of the effects of changes of pressure on the behaviour of marine animals is described.

In 43 of a total of 53 species examined in this apparatus definite responses to abrupt pressure changes of 1000 millibars or less have been observed, increased pressure generally causing increased activity and movement upwards or towards the light, and decreased pressure causing decreased activity and movement downwards or away from the light. The relative importance of light and gravity in the orientation of these movements is generally correlated with the degree of development of the light and gravity receptors in the species concerned.

The possible significance of these pressure responses in nature is discussed and it is suggested that pressure may be an important factor affecting the distribution of marine plankton, particularly during the hours of darkness.

The biology of whiting in Manx waters has been investigated at different stages of the life-cycle, with special reference to their diet. Planktonic postlarvae occurred chiefly in May, these measured between 4.5 and 16.5 mm, and had fed chiefly on Pseudocalanus. Larger whiting (between 21 and 52 mm) were taken in association with Rhizostoma. They were approximately 2–4 months old, and had fed on copepods supplemented with Hyperia and euphausiid furcilia. Immature whiting 77 mm long appeared in July in a shallow sandy bay—a nursery area. The fish were about 4–5 months old, and fed on swarming amphipods, isopods and mysids after dark, when these organisms were free-swimming. This diet was supplemented to an appreciable extent during the following April-June quarter by the inclusion of juvenile Ammodytes. After staying for nearly 1 year in the nursery area, the bulk of the fish appear to migrate to the open sea.

In the open-sea habitat, the immature fish fed chiefly on euphausiids, decapods and sprats—nektonic forms particularly. These whiting are themselves eaten by larger whiting in the same habitat. Adult whiting (over 220 mm) were taken only offshore, and fed chiefly on euphausiids, Crangon, Pandalus, Pasiphaea, Clupea and gadoids. A few samples taken off the east coast of I.o.M. indicated that the whiting are capable of feeding on infauna and plankton in an environment deficient in active epifauna and nekton. The whiting is an active feeder throughout the year.

Two length-weight relationships have been calculated for Manx whiting: nursery-area, and open-sea fish—the latter gain weight more rapidly than the former would be expected to do.

Gases from the chambers of the cuttlebone have been analysed. Their partial pressures were never higher than those expected in the tissues of the animals.

In the older chambers the gas was about 97 % N2. The pressure of the gas in these chambers is always close to 0.8 atm.

These results are in accord with the theory that the gases play an unimportant role in the mechanism of the cuttlebone and merely diffuse into spaces created by forces other than gas pressure.

Observations have been made which can be used in studies of the life history and the rates of growth of cuttlefish in the Channel.

A new species provisionally attributed to the genus Nephroselmis has been described with the aid of light- and electron-microscopy. Significant features include the presence of a single layer of scales over the flagellar and cell surfaces as in Micromonas squamata Manton & Parke, though the morphology of the flagellar scales is as in the outer scale layer of Pyramimonas and Halosphaera. Reasons are given for rejection of Thalassomonas on the grounds of nomen confusum and for homologizing various representatives of it with Micromonas squamata.

Some additional facts about the latter include details of the imbrication of the flagellar scales and demonstration, made possible by the use of lead staining of sections, of a close association between golgi bodies and the scale-producing vesicles.

1. A study of the histology of the eyes of some cartilaginous fishes has been made with special reference to their reflecting tapeta.

2. The rate and way in which the pigment in the melanophores spreads over the reflecting cells of the tapetum of Squalus acanthias when it is lightadapted are described.

3. The reflecting plates in the tapeta are about parallel to the plane of the retina in the centre of the eye, but as we move towards the periphery they become more oblique, until near the ora they are almost perpendicular to the plane of the retina. It is shown that when we take account of the way in which the pupil limits the light which can reach the retina in all these situations the plates are arranged to be roughly perpendicular to the incident light. They reflect light either back through the pupil or on to the very black inside surface of the iris and do not scatter it to other parts of the eye.

4. The reflectivity of tapeta for various angles and various wave-lengths of light has been found by several different methods, and a new and simple way of measuring the reflectivity of natural tissues is described. For the blue and green lights which will be those reaching the eye in life the reflectivity is very high, over 80%, and so approaches that of a good metallic mirror.

5. The external segments of the retinal rods of cartilaginous fishes which have well-developed tapeta are only about half as long as those of other fish living in the same environment, and the retinal optical densities of photosensitive pigments in these fish are only about a half of those of fish without reflecting tapeta.

The uptake of 134Cs by 36 species of marine and freshwater fish and shellfish has been measured, and for selected species has been shown to depend on a power of the weight. For plaice, lobster, and eel, over thousand-fold ranges of weight, the uptake varies according to ω0.78. The times taken to reach half-equilibrium concentrations vary according to a value between ω0.25 and ω0.29, e.g. for a 100-fold increase in weight there is a 3.5-fold increase in half-value time.