Preliminary culture assays were made using marine algae to elucidate the ‘quality’ of sea waters from the North Sea and North Atlantic Ocean for phytoplankton growth. Assays with (a) bacteria-free Skeletonema costatum, (b) unialgal Skeletonema and Peridinium trochoideum and (c) mixed phytoplankton organisms indicated change of quality according to location, depth and season. Assay results correlated best with zooplankton indicator quality and to a lesser extent with phytoplankton abundance. Assay results were also compared with the distributions of temperature, salinity, oxygen, phosphate, U.V. fluorescence, phytoplankton dominants, zooplankton dominants and abundance. Assessment of sea-water quality was biased for the assay organism used. Factors which altered sea-water quality were added thiamine and B12 (40% improved), IAA (25% improved) and EDTA (almost invariable manyfold improvement). Destructive chemical treatments removed almost completely any good qualities for growth of Skeletonema but seldom for that of Peridinium.

Entobdella soleae, a monogenean skin parasite of the common sole was induced to feed on its host. The feeding organ (,pharynx-) is protruded during feeding and encloses a circular area of host skin. The gland cells in the feeding organ produce a proteolytic secretion which digests the epidermis of the fish. The liquid food is then pumped by the feeding organ into the intestinal diverticula, where it is absorbed.

Acanthocotyle sp. from the skin of an elasmobranch fish, Raia clavata, feeds on epidermis in the same way as Entobdella soleae. Observations on other skin and gill-parasitic monopisthocotylineans indicate that the majority of them are epidermis feeders, although there is evidence that some gill parasites, for example Amphibdella torpedinis, may feed on blood.

The evolution of parasitism in the Monogenea is tentatively attributed to the outstanding qualities offish epidermis as a food for a potential ectoparasite and in particular to its rapid rate of regeneration.

This paper is concerned with the number of eggs in the roes of ripening female plaice, Pleuronectes platessa L., caught off La Rochelle during the winter of 1960–61. The fecundity of plaice has been studied over a number of years in fish collected over a wide area (Bagenal, 1958,19600,6,1962) and the results given in this paper apply to plaice caught as near the southern limit of their distribution as possible. Although plaice have been recorded from farther south (Wimpenny, 1953), La Rochelle is the most southerly port where they can be obtained in sufficient numbers.

The history of the medusa Tiaranna rotunda (Quoy & Gaimard) is reviewed. Little has been published on its young stages and its hydroid is unknown.

Young specimens of the medusa, caught in the Firth of Clyde, are described and figured.

The species Modeeria formosa Forbes is discussed and is shown to have been described from a young specimen of Tiaranna rotunda. By priority the specific name becomes Modeeria rotunda (Quoy & Gaimard), and Modeeria Forbes becomes a senior synonym of Tiaranna Haeckel. The family name Tiarannidae is unchanged. The type-genus is Modeeria, of which the typespecies is M. rotunda.

The seasonal occurrence of the medusa is discussed and evidence is adduced supporting the belief that the species is specialized for living in deeper water.

Six species of algae, Chlorella marina Butcher, Dunaliella tertiolecta Butcher, Isochrysis galbana Parke, Monochrysis lutheri Droop, Phaeodactylum tricornutum Bohlin and Hemiselmis virescens Droop were fed to oyster larvae in bacteria-free culture. In addition, cultures of Chlorella stigmatophora Butcher, Isochrysis galbana and Phaeodactylum tricornutum containing bacteria were also used. Cultures of galbana containing bacteria were used as controls in all series of experiments. In each series various densities of food, expressed both as cell numbers and as packed cell volume, were fed to the larvae of Ostrea edulis L. for 22–46 h and the change in the mean size of the larval population was used as the index of the value of the food.

The experiments with Chlorella confirmed previous work that organisms of this genus have little value as food for larvae. With Dunaliella and Phaeodactylum growth was better at low food densities with some (but not all) batches of larvae compared with Isochrysis. The comparison of cultures of Isochrysis and Phaeodactylum with and without bacteria showed no consistent improved growth with either food. Monochrysis had about the same food value as Isochrysis. With Hemiselmis some growth was obtained but not as much as with Isochrysis.

Variation in size of fossil euryhaline ostracods is discussed and compared to size variation in recent forms. The most likely cause of variation in size of euryhaline ostracods is variation in salinity. Similarities are indicated between Fabanella and Cyprideis species.

This paper is one of a series on the fecundity of the plaice Pleuronectes platessa L. over a wide area of its geographical distribution and is concerned with the number of ripening eggs in the roes of female Icelandic plaice prior to spawning (see Bagenal, 1962, for references to other areas).

Thirty-eight plaice were caught by the Icelandic research vessel ‘Maria Julia’ on 23 and 24 March 1961 in the Midnessjor area. They were measured and weighed and the otoliths were extracted. The ovaries were preserved in modified Gilson's fluid (Simpson, 1951). I am very grateful to Mr Jon Jonsson who kindly made all the arrangements and Mr Gunnar Joakimsson who prepared the material in Iceland. The fish were very ripe and a few had developed translucent eggs, but spawning had not begun. The subsampling and statistical treatment of the results were the same as before (Bagenal, 1962). The otoliths, after being kept dry, were very difficult to read.

The Icelandic plaice are an isolated population, separated by deep water from the rest of Europe, and there are several spawning areas. currents move clockwise round Iceland and will carry the fertilized eggs and young larvae from Midnessjor and the S.W. coast spawning areas (Thomsen, 1948) to the good nursery grounds of Faxa Bay. Tåning (1929, 1948) has given accounts of the Faxa Bay plaice biology and suggests that ‘the eggs and tiny fry, which are found in the Bay in the spring months, seem mainly to come from the outside, for the greater part most probably from S.W. Iceland’. The eggs from the population offish considered in this paper, from Midnessjór, would drift into Faxa Bay which forms a good nursery ground.

On British shores Pylaiella littoralis occurs in a large number of local populations which usually fall into one or other of four population groups. These populations often differ in habit, form, seasonal distribution, etc.

Two populations of P. littoralis from different environments have been studied experimentally and it seems from this that the morphological differences between the plants from the two populations are accompanied by physiological and genetical differences. Similar results have been obtained from experiments on other populations.

It is suggested that the numerous populations arise through the selective effect of all the prevailing environmental factors and are adapted to them.

The potentially large number of plant forms resulting from this process should not be described in terms of ‘orthodox’ taxonomy though they may possibly merit definition in terms of ‘experimental’ taxonomy in so far as some of the populations may constitute ecotypes as recognized in higher plants. Because it is possible for a single ecotype to be represented by more than one morphological type, however, the value of the ‘experimental’ system is regarded as doubtful.

The seasonal changes in the body weight and composition of two common boreo-arctic species of cirripedes, Balanus balanoides and B. balanus have been followed.

At a constant size (age under constant growth conditions) the body weight is closely related to the season. Increase in body weight takes place rapidly during the spring as reserves are laid down. These reserves are subsequently utilized for gonadal development.

The changes in B. balanus are more gradual than in B. balanoides and probably reflect differences in the habitat conditions.

The reserves, although contributing to the gonads, are not themselves adequate for their total tissue.

Amino acids, both free and combined as protein, and some other nitrogenous constituents of Calanus finmarchicus have been examined. Seventy-six per cent of the total nitrogen in C. finmarchicus was present in protein amino acids, 14% in the free amino acid fraction, 6% in trimethylamine oxide, and 1·5% in betaine. These findings are discussed in relation to previous work on nitrogenous constituents of Calanus.

The free amino acid fraction of Calanus is compared with that of higher Crustacea and it is suggested that this fraction may be important in the adaptation of the animal to dilute sea water.

Amino acid nitrogen made up 40% of the total nitrogen of particulate material from Clyde sea water. This finding is compared with other recent analyses of the phytoplanktonic nitrogen and total particulate nitrogen of inshore waters.

Larger algae and protozoa plankton of inshore waters seem generally well known, except for a few groups of very small flagellates. The same statement cannot be made for the micro-organisms of the bottom sediment-water interfaces and intertidal sand. Many ecologists and physiologists would like to know more about what species and how many individuals can be expected in such locations as these.

The amino acid composition of adult female Calanus helgolandicus Claus and particulate material at station L4 has been analysed from March to December. The average concentration of amino acid nitrogen in Calanus was 7·7% of the dry body weight and accounted for 83% of the total nitrogen. The average level of amino acid nitrogen in the particulate material was 11·9 μg/1. and accounted for 54% of the total nitrogen.

The relative quantities of amino acids in Calanus remained remarkably constant throughout the year. The relative quantities of amino acids in particulate material were more variable.

The rate of respiration of Calanus measured at 8°C varied from 31 μl. O2/mg. dry body weight/day in winter (December–February) to 79 μl. O2/mg dry body weight/day in summer (April–August).

Starving winter Calanus lost 1·8% and starving summer Calanus 2·1% of their dry body weight as amino acids each day. In order to replenish its daily losses of amino acids winter Calanus must sustain a filtering rate of about 30 ml./animal/day: the corresponding value in summer is greater than 50 ml./animal/day.

The amino acid composition of Skeletonema costatum is so close to that of the particulate material in the sea, that, as far as amino acids are concerned, Calanus would gain no nutritional advantage by selecting the diatom in preference to the amino acid containing fraction of particulate material as a whole.

There is some reduction in oxygen uptake of isolated bodies on starvation when carbohydrate is being utilized.

There is a gross discrepancy between the oxygen demand as measured in isolated bodies and the available substrate; respiration is probably reduced during inanition.

It is suggested that the moulting cycle is coupled to the metabolic activity in an obligatory fashion rather than being dominated by the kind of hormonal control found in decapods.

The entire cell surface, including the flagellar surfaces, of three species of Pyramimonas and of two different strains of Pyramimonas-hke zooids of Halosphaera are shown to be covered with scales in at least two layers, namely, an underlayer of very small scales arranged directly on the flagella membrane or plasmalemma and one or more outer layers of much larger scales of different character. On one and the same cell the shapes of the scales of all layers are different on the flagella from those on the body. Among all the taxa studied the flagella scales are very similar but those of the bodies are specifically differentiated; details are illustrated in the plates. In two taxa {Halosphaera and Pyramimonas amylifera) the outer scales on the flagella have been shown to be consistently arranged in 9 longitudinal rows; numerical information is not available for the other taxa studied but they are not expected to be different. The presence of an unusual type of flagellar hair has also been noted though those have not yet been studied in detail.

A description is given of Siboglinum holmei sp.nov., a shallow-water Atlantic species. It is compared with S. caulleryi, a related species from the Pacific.

The accumulation of radioactive Cs has been studied in species from the principal marine invertebrate phyla. In some species the accumulation of radioactive Cs has been compared with that of 42K and equilibrium levels of both isotopes have been related to the distribution of inactive K.

Radioactive Cs is always absorbed more slowly than 42K. Most of the inactive K is readily exchangeable with 42K so that at equilibrium inactive and active concentration factors are nearly equal. Whole animal concentration factors for radioactive Cs at equilibrium varied between 1·2 and 14 in unfed animals. These factors usually exceed those for inactive K because, although body fluid concentration factors are similar for both ions, the tissue/body fluid ratios for radioactive Cs exceed those for inactive K. Radioactive Cs penetrates rapidly into body fluids, so that uptake by the tissues is the limiting factor in accumulation. Although Cs is absorbed much more slowly than K, the eventual distribution of Cs between the tissues and body fluid of a particular species appears to bear a relationship to the distribution of K.

No evidence has been found to suggest that Cs is a necessary element which is absorbed specifically.

The interstitial archiannelid Trilobodrilus heideri was found to be photophobic, fairly tolerant of low salinities and responsive to water current. This latter response of orientation and progression toward a water source was gradually lost by specimens suddenly transferred to low salinities. Rhythmic gregariousness was shown to occur in this species. The relation of this rhythm to tidal factors is postulated. It is shown how the demonstrated responses may affect the position occupied by T. heideri on the shore