An account has been given (Harris, 1972b) of the distribution of interstitial harpacticoid copepods on an intertidal transect at Whitsand Bay, E. Cornwall. The present work describes seasonal changes observed in the copepod species populations over a period of 2 years, from May 1968 to May 1970. Changes in population density and vertical distribution are described, and the relationship between these changes and the physical environment are discussed. A full account of the reproductive activity and lifecycles of the copepod species will be given later (Harris, 1972d). The only detailed accounts of seasonal cycles of individual intertidal harpacticoids are those of Lasker, Wells & Mclntyre (1970) for the sand-dwelling benthic copepod Asellopsis intermedia (T. Scott) and of Barnett (1968, 1970) for two species of Platychelipus Brady on an intertidal mudflat.

Information on the reproduction of interstitial harpacticoid copepods is mainly restricted to occasional references in the taxonomic literature to the presence of ovigerous females in collections. C. G. Rao (1967) provides the only account of the life-history of an exclusively interstitial species. The only detailed field study of seasonal reproductive cycles of harpacticoid copepods are of two species of Platychelipus Brady on a mudflat (Barnett, 1970), and of a sand-dwelling benthic copepod, Asellopsis intermedia (T. Scott) (Lasker, Wells & Mclntyre, 1970).

This paper is the third of four dealing with the calanoid copepods taken with a modified Indian Ocean Standard Net (N113H) on the R.R.S. 'Discovery' SOND cruise of 1965. Details of the cruise are given by Currie, Boden & Kampa (1969) and the sampling methods used in the N113 H series are described by Foxton (1969) and by Angel (1969).

A dredge equipped with a gate which may be opened by a diver-monitor when it is passing over bottom selected for study and closed elsewhere is described. A meter wheel which activates an electric switch, connected with a battery and counter in the boat, is in contact with the bottom when the gate is open and raised from the bottom when it is closed. This permits the taking of sampling units of uniform predetermined size. Field trials demonstrated that the dredge efficiently captured all categories of animals large enough to be retained by its meshes.

The difficulty of obtaining unbiased, representative samples of single populations is compounded by the complexities of aggregates of populations, such as biotic communities, and even more by discontinuities in the dispersion of the constituent species and the habitats in which they live. The probability of taking such unbiased, representative samples of marine communities decreases with the depth of water from which they are obtained. Sampling confidence at a level which may be taken for granted in terrestrial habitats is possible only in the littoral and shallow sublittoral. And this is true only if the investigator is able to assure himself that each sampling unit is excised only from the kind of habitat whose biota he wishes to study. He may achieve this specificity in sampling benthos, for example, by using grabs and discarding material brought up from bottom types not under investigation. Another approach is to engage in a comprehensive, preliminary, systematic exploration so that when he samples for parametric estimates he can place his grab exactly where he knows that the desired habitat exists.

The biology of the bass in British and Irish waters has not been studied in the same detail as the biology of commercially important species, such as gadoids, flatfishes, mackerel and herring.

Twenty-four out of 240 fishes caught by bottom lines at 366–3333 m had something in their stomachs. Stomach contents included parts of cephalopods, fish, cetaceans and bottom-living invertebrates, thin rubber sheet and terrestrial mammal bones. The material provides evidence that four species of cephalopod are at least partially demersal and suggests a means by which the tapeworm Phyllobothrium could pass from its secondary to its primary host.

During the five biological cruises of R.R.S. ‘Discovery’ between 1967 and 1971 a total of 31 bottom lines with 1483 hooks were fished in depths of water between 366 and 3333 m. The stomachs of the 240 fish caught were examined and 216 (90%) proved to be empty. The high incidence of empty stomachs is thought to be due to frequent loss of food during the ascent from great depths and accounts for our poor knowledge of the feeding habits of demersal fish living at depths exceeding 400 m.

The present collection of food from 25 stomachs (24 from ‘Discovery’ collections and one from a fish caught by Mr G. R. Forster from R. V. ‘Sarsia’) of fish belonging to 11 species (Table 1) probably gives little indication of the usual diet of the fish concerned, but its nature prompts some useful speculation and the rarity of such observations justifies placing them on record (Bigelow & Schroeder, 1948; Marshall, 1954).

All the fish were caught on lines which lay on the bottom for several hours and it is our firm belief that they were hooked while on or very near the bottom.

According to the generally adopted view, all the proprioceptors of the leg articulations of decapod Crustacea respond to stretching or relaxation of the organs caused by joint movements or joint position. This view is based on anatomical and physiological studies made, originally, mostly on crabs. It has been found, however, that in other groups of Crustacea, such as Anomura and Macrura Reptantia, some of these receptor organs are anatomically related to structures on the exoskeleton. This type of receptor organ, examined in Palinurus vulgaris Latreille, Homarus gammarus (L.) and Pagurus bernhardus (L.), is the main subject of the present paper. In the course of this work some observations have been made on other proprioceptors, particularly those in the ischiopodite-meropodite articulation, and these too are reported below. The organs in the coxal region, the special structure of which was the subject of previous investigations (Alexandrowicz & Whitear, 1957; Alexandrowicz, 1958, 1967), are not included.

Changes in blood glucose levels in teleosts have been reviewed by a number of workers. Epple (1969) considered the regulation of glucose by the insulin of the fish pancreatic islet tissue, Nakano & Tomlinson (1967) examined the regulation of glucose by the catecholamines, Black, Robertson & Parker (1961) considered glucose in carbohydrate metabolism of teleost muscle, while knowledge of regulation of blood glucose in Chondrichthyans has recently been extended and reviewed by Patent (1968, 1970). The investigation of blood glucose levels and their control mechanisms dealt with in this paper forms part of a broader study of the changes that occur when fish are caught from the wild and placed in aquaria (Wardle, 1968, 1971, and unpublished). In this study, capture is considered as a stimulus imposed on the wild fish, which initiates a series of physiological changes that can be measured as the fish adapts to the aquarium.

The sense organs of the lateral-line system of lower aquatic vertebrates are mechanoreceptors which respond to water movements. They are distributed over the body, usually in lines which form a definite pattern on the head and along each side of the trunk. In the Cyclostomes the sense organs project from the body surface ('free neuromasts'); in other aquatic vertebrates they are usually housed in canals which are sunk into the dermis and which open at regular intervals to the exterior, although in some teleosts and in all modern amphibia the canal system has been secondarily lost and the neuromasts are once again situated externally.

Aspects of the physiology of the two cockles Cerastoderma edule (L.) and C. glaucum (Poiret) in air have been investigated. Both cockles exhibit bradycardia during exposure and are similarly tolerant of anoxic conditions, but C. edule survives longer in air than C. glaucum. This is accounted for by the fact that C. edule displays a behaviour pattern of valve movements upon emersion which allows air-breathing. Oxygen uptake rates of this cockle measured in air lie close to the lowest rates recorded in water, and are considered to approximate to a basal or quiescent level. C. glaucum does not air-breathe and is restricted to lowest shore levels. Values for ‘maximal’ levels of oxygen uptake in water have also been obtained together with estimates of metabolic scope for the cockle.

An initial report is presented on some chemical properties of the waters in the Tamar Estuary. The results are compared to those obtained in the Western Channel during the same period. Considerable differences are shown in the concentrations of inorganic nutrients but the dissolved organic nitrogen concentrations are relatively similar. Dissolved iron has been estimated both before and after the breakdown of organic compounds by photocombustion. The results show the build-up of humic substances and associated iron after heavy rain. When the concentration of suspended sediment in the water is high it can control the level of dissolved phosphorus by removing it from rich water and releasing phosphorus into poor waters.

Adult males of Nereis virens (Sars) spawn while swarming in mid-water and show epitokous changes which include enlarged parapodia, natatory chaetae and histolysis of the body wall. Females spawn while in their burrows and do not show such changes. An artificial rise in temperature can induce premature spawning. Seminal fluid is ejected through pygidial pores, but no such pores occur in the female. Both lunar period and temperature rise seem to be involved in initiating spawning, which generally occurs in early May in the Thames populations. Gravid worms show a peculiar method of swimming in which the anterior region is held rigid. A pair of flagellar vanes and other features characterize the fine structure of the spermatozoon. The mature oocytes bear microvilli, and some express a jelly-like layer after fertilization which traps excess spermatozoa. Many unit-membraned vesicles, of uncertain function, occur in the periphery of the nucleus of the mature oocyte. At fertilization the acrosomal contents are discharged on to the surface of the oocyte. The structure and behaviour of the monotrochophore, trochophore and nectochaete larvae, and the details of the nature and rate of development of such structures as the parapodia, cirri, palps and jaws, differ in some ways from the known larval development of certain other nereids. A very brief planktonic phase occurs in larval life, and young worms migrate from the sublittoral to the littoral regions.

The permeability properties of the silvery walls of the swimbladders of eels (Conger conger and Anguilla anguilld) have been studied. The intact swimbladder wall is very much more impermeable to carbon dioxide, oxygen and nitrogen than ordinary connective tissue. Removal of the silvery layer of the wall, which contains crystals of guanine with a little hypoxanthine, increases the permeability about 100 times and leaves a transparent ‘epithelial’ layer only a little less permeable than connective tissue to these gases. The wall of the pneumatic duct of the conger swimbladder, which is not silvered, has permeability properties similar to those of connective tissue. In long-lasting experiments a production of carbon dioxide not coupled to oxygen usage was detected in the epithelial layer. The ratios between the diffusion constants of CO, N and O for both the silvery and epithelial layers show that diffusion probably takes place through water-filled pathways, and calculations show that impermeable overlapping crystals embedded in the silvery layer could account for its very low permeability. Two deep-sea eels were shown to have swimbladders whose walls contained about 10 times more guanine/unit area than the conger eel. The possibility that layers of guanine crystals may divide fish into compartments is discussed.

The polychaete Polyphysia crassa (Oersted) is unusual in possessing a well-developed body-wall connective-tissue layer which exceeds the combined thickness of the circular and longitudinal muscles. Both collagenous and elastic fibres are present in this layer. The collagen is organized as a loose three-dimensional lattice allowing longitudinal, circumferential or radial distension of the body wall and, as in other soft-bodied invertebrates, serves the functions of providing a base on which the muscles can act and of imposing limits to the extensibility of the system. The elastic fibres are organized as an apparently randomly oriented meshwork of stout fibres around the circular muscle blocks and are attached to both the circular and longitudinal muscles. Columns of elastic fibres extend radially from the supramuscular coarse meshwork through the ‘holes’ in the collagen lattice to the epidermal basement membrane. As the elastic columns extend outwards the fibres become finer and more numerous and flute out to give a wide area attachment to the epidermal basement membrane. The radial elastic columns are cross-linked by tangential elastic fibres. Although at any point the main collagen and elasticfibre bundles are oriented at right angles to one another, collagen fibres are invariably associated with the elastic fibres and the two fibre types form a single functionally inte-grated system. Polyphysia lives in flocculent, sublittoral muds and the burrowing mechanism employed involves a pronounced direct peristaltic wave of simultaneous circular and longitudinal muscle contraction which necessitates considerable radial thickening of the body wall. The functions of the elastic fibres appear to be to oppose the radial distension of the body wall which the collagen lattice permits and to control the folding of the cuticle and epidermis and the return of the collagen system after the passage of a peristaltic wave.

Some preliminary experiments are described which indicate that the larvae of Scrupocellaria reptans (L.), Spirorbis corallinae de Silva and Knight-Jones forma reptans l'Hardy and Quiévreux and Spirorbis (Janua) pagenstecheri Quatrefages prefer to settle on the younger parts of the fronds of Laminaria digitata (Huds.) Lamour. Two possible explanations for the ecological significance of this behaviour are discussed and some supporting evidence is given.