The quantitative study of phytoplankton production may be pursued in many ways, but these ways can be divided into two general methods of approach. There is, first, the direct estimation of a production rate for a particular sample of the population; for example, the light-dark bottle technique for measuring oxygen production (Gaarder & Gran, 1927; Riley, 1939) and the new 14C technique (Steeman Nielsen, 1952). These estimates are made under conditions which must be, to some extent, artificial. Secondly, there is the direct estimation of relevant variables in the sea (phosphate, oxygen, chlorophyll concentration, etc.) from which production is calculated on the basis of hypotheses about the behaviour of phytoplankton. These hypotheses are, of necessity, simplifications of a mass of laboratory experiments and of previous field work. Riley, Stommel & Bumpus (1949) give a full account of this approach and of the difficulties involved in it.

The sudden appearance of Akera bullata in the static water tanks of H.M. Dockyard, Devonport, provided specimens for the investigation of pigments. Morton & Holme (1955) have given an account of certain aspects of the biology of this interesting tectibranch mollusc.

Apart from a general account (Kon, 1954) of our work on vitamin A and carotenoids in invertebrates, our publications so far (Kon & Thompson, 1949a, b; Batham, Fisher, Henry, Kon & Thompson, 1951; Fisher, Kon & Thompson, 1951, 1952, 1953, 1954, 1955) have been concerned only with marine Crustacea. We have also studied, during our investigation of the metabolism of vitamin A and its possible precursors in the sea, numerous species from most other phyla of marine invertebrates. Except for the nematode worm, Anisakis physeteris Baylis, taken from the stomach of a sperm whale, the only two phyla of invertebrate animals in which we have so far found vitamin A are the Arthropoda and the Mollusca. The vitamin was present in at least some species from each of the molluscan classes, Loricata, Gastropoda, Lamellibranchiata and Cephalopoda, but we have no information yet about the Solenogastres or the Scaphopoda of which we have analysed no representatives. So far as our studies were concerned, the cephalopods differed considerably from the other molluscs examined, and the relatively large amount of information they have provided will be more conveniently presented in a subsequent paper. The account which follows, therefore, deals only with species from the first three classes just listed.

In our previous paper (Fisher, Kon & Thompson, 1956) on Mollusca we pointed out that the Cephalopoda were so different from the other classes in vitamin A and carotenoid relationships that they would be more satisfactorily considered separately. We have so far analysed ten species of cephalopods and found vitamin A in all of them. The studies of previous investigators of vitamin A in these molluscs were confined to its function in the visual cycle and to its contribution to the vitamin A reserves of sperm whales feeding on cephalopods. The carotenoids of cephalopods have been given even less attention than vitamin A.

The polychaete Nereis diversicolor F. O. Müller is one of the most characteristic elements of the brackish-water fauna of north-western Europe, and inhabits an extremely wide range of salinities. As a background for comparative physiological studies of chloride regulation in worms from different parts of the geographical range, the writer has attempted to describe the salinities and the variations in salinity endured by populations of N. diversicolor in eco-logically distinct and geographically well separated areas. Three principal environments have been studied:

Maas (1903) described two specimens of a deep-water coronate scyphomedusa collected on the Siboga Expedition in the Malay Archipelago. He erected for these a new genus Paraphyllina and called the species P. intermedia. It differed from Periphylla in that the rhopalia were perradial and not interradial. In 1903, Lo Bianco figured a specimen taken in the Mediterranean near Capri which was identified for him by Maas as P. dodecdbostrycha (see also Maas, 1904, p. 48, footnote); Mayer (1910) saw this specimen and re-described and figured it as Paraphyllina intermedia. A fourth specimen ascribed to this species by Ranson (1936) was found washed up on the shore at Villefranche.

In recent years there have been several accounts of the occurrence of diclidophoroidean trematodes parasitic on the gills of fishes, e.g. Price (1943), Sproston (1946), Dawes (1947), Brinkmann (1952), and Chauhan (1953), and these accounts have included descriptions of the morphology of the parasites. The distribution records have revealed a generally high degree of host specificity and, in some species, a preference even for certain gill arches of the particular hosts, while the morphological descriptions have shown that there is a considerable variation in the form of the parasites, extending to various degrees of deviation from bilateral symmetry (PI. I, figs. 1–11). These morpho-logical variations are present in spite of the fact that the different parasites occupy such broadly similar habitats in the gill chambers of their respective hosts. But, as far as I am aware, this is the first attempt to investigate the distribution and morphology of the parasites in relation to their micro-habitats.

In continuation of the studies on receptor elements in the Crustacea the common prawn, Leander serratus, has been investigated by the methylene-blue method applied in the same way as described in an earlier publication (Alexandrowicz, 1951). It has been found that there are in Leander receptors of the same kind as in those crustaceans previously investigated, some of which exhibit features not yet observed before. As in other crustaceans they are similarly situated on the dorsal side of the body, but since a knowledge of the disposition of the dorsal muscles in the thorax and the abdomen is necessary for locating them, some data about the topography of the muscles are first given.

At the time of his death in 1953 Orton had almost completed an extensive study of the biology of the three British species of Patella. Although certain aspects of the investigation were dealt with by collaborators and have already been published (Crewe, 1947 on parasites; Goodwin, 1950 on pigments; Jones, 1948 on ecology) most of the breeding and spawning data have been neither analysed nor published. With the knowledge that Orton's records contained the most complete information on breeding yet compiled for a littoral animal, and that these records had considerable bearing on the question of speciation in Patella, we have attempted to analyse and present those which are most complete.

Some preliminary observations in North Cornwall (Orton, 1946) showed that the periods of breeding of the three British species of limpets were different. In order to determine these differences more accurately, and to study the breeding cycle, samples of limpets from six localities in Britain were examined at regular intervals for 5 years. This paper gives the results obtained for the common limpet Patella vulgata, which was present at all the localities sampled and was the most intensively studied of the three species. Later papers will deal with the remaining species and with other aspects of the investigations.

We know that a mature female plaice can liberate many thousands of eggs into the sea during the spring spawning season in the southern North Sea (Simpson, 1951). We also know that a very small percentage indeed of these eggs develops into fish of marketable size. At all stages in its life history a plaice is con-fronted with environmental hazards, which, if not overcome, may have fatal consequences.

The present study had two aims: first to seek among the molluscs of the Plymouth region, one with a heart suitable for the bioassay of acetylcholine and 5-hydroxytryptamine; and secondly, to examine moUuscan nervous tissue for the presence of cardio-regulator substances. Brief reports of some of the results have appeared elsewhere (Welsh, 1953a, 1954a).

The endostyle of Amphioxus has for a long time been regarded as homologous with the subpharyngeal gland of the cyclostome ammocoete larva. This view was promulgated by Müller (1873) and by Dohrn (1886), and has been supported by many workers, for example Leach (1944). The metamorphosis of portions of the subpharyngeal gland to the thyroid gland of the adult lamprey was followed by Marine (1913), and uptake of radioactive iodine by certain cell elements of the subpharyngeal gland was demonstrated by Gorbman & Creaser (1942). At the same time the latter workers failed to establish the presence of iodine in the endostyle of Amphioxus by autoradio-graphic techniques. Gorbman (1941), however, showed that the ascidian Perophora annectans could accumulate radioactive iodine in its pharyngeal stolon but not in its endostyle. The part of the pharyngeal stolon involved is derived from the endostylar region of the pharynx. Recently, Sembrat (1953) has shown that endostyles of Amphioxus implanted into larval axolotls accelerated their metamorphosis, and concludes from this that the organs contain an ‘active substance (or substances) which may evoke amphibian metamorphosis similarly to the active hormone of the thyroid gland. It is probable that the substance is not identical with thyroxin which may be inferred from the fact that the endostyle’ of Branchiostoma does not accumulate radioactive iodine (Gorbman & Creaser, 1942) as well as from its different and tolerably little efficacious influence on the amphibian metamorphosis as compared with typical metamorphic symptoms induced by the thyroid gland.’ The work about to be described has demonstrated the presence of iodine in the endostyle, and suggests, further, that it is present in the form of a ‘thyroid hormone-like’ substance, thereby supporting Sembrat's general conclusion.

It is well known that towards the limits of an animal's geographical range both its abundance and exact boundaries may fluctuate from time to time. These fluctuations can sometimes be correlated with environmental changes, and thus may help to assess the relative importance of the factors that control distribution. For example the distribution of the common intertidal barnacles Chthamalus stellatus (Poli) and Balanus balanoides (Linnaeus) underwent changes which were attributed to a general rise in temperature over several years (Southward & Crisp, 1954a). The abundance of these barnacles has fluctuated further since 1951–52, and we are now able to analyse more closely the relation between the population changes and environmental variations.

A number of records from echo-sounders have been loosely attributed to the presence of plankton. Only two records have been adequately identified as having been produced by plankton; first, the traces offish larvae, or shallow scattering layers (Burd & Lee, 1951); and secondly, the echo layer, at the depth of the temperature discontinuity or thermocline, which is sometimes associated with plankton animals or plants (Cushing, Lee & Richardson, in press). A third type of record, that from the ‘deep scattering layer', has been associated with the presence of euphausiids (Hersey & Moore, 1948; Moore, 1950; Boden, 1950): an equally plausible association with the presence of fish has been made by Marshall (1951), Tucker (1951) and Hersey & Backus (1954). A fourth type of echo record, a ‘noisy’ record, will be described and will show that it is probably attributable to plankton organisms, consisting, in one instance, of euphausiids.

Lasaea rubra is the smallest and commonest of Plymouth bivalves. It is intertidal on rocky shores, often in immense numbers, in crevices and other protected places, and in Pygmaea pumila (Colman, 1940). This bivalve is an excellent laboratory animal. It remains fully active for several days under laboratory conditions, and a large number of animals can be used in a single experiment, eliminating the variations in activity found when dealing with a few, or single specimens of larger animals. Because of the relatively high position Lasaea rubra may occupy on the shore its feeding cycle is broken by regular dry periods at each tide. Thus, for experiments relating to periodicity in feeding, we have an animal whose times of feeding can easily be ascertained and experimentally varied over a wide range. Lastly, in making serial sections and in examining total gut contents, in work on the digestive system, the small size of the animal is of obvious advantage.

Fish eggs can be divided into three main groups: marine pelagic eggs which float of their own accord, marine demersal, and freshwater demersal eggs. The embryological development of freshwater teleosts follows an accepted pattern, demonstrated by morphologists during the nineteenth century. Marine embryos, both pelagic and demersal, do not conform in all respects to this pattern, and misunderstandings have frequently arisen by lack of attention to known structural differences between the three groups. Mclntosh & Prince (1890), in their comprehensive review offish development, emphasized some outstanding anomalies in pelagic structure, but gave no adequate explanation of their occurrence.