Data are given on the abundance of post-larval stages of teleostean fish in half-hour oblique hauls with the 2-metre stramin ring-trawl taken at weekly intervals at a position two miles east of the Eddystone lighthouse during the years 1930 to 1934 inclusive.

The seasonal composition of the catches is considered and it is shown that there is a gradual change over from the young of northern species of fish to those of more southern species as the summer advances. The relation between the spawning times of closely related species appears usually to be a function of their geographic distribution.

The period of maximum abundance of post-larvæ of spring-spawning fish occurs at different times in different years and this difference may be as much as a month. An apparent correlation between the times of abundance of young whiting and the previous temperature of the water has been shown.

Studies are reported of the behaviour of stored sea-water with regard to oxygen, ammonia, and bacteria content in relation to the conditions of storage and to the effect of various filtration procedures.

When sea-water is sterilised by filtration and stored in the dark, the oxygen content remains constant or diminishes only by less than 0·07c.c. per litre in several hundred hours.

In non-sterile experiments there is always an oxygen consumption roughly parallel to a bacterial multiplication which begins very suddenly after collection of the water. These effects are greatest in “raw” water, less in paper-filtered water and least in water which is doubly filtered.

Samples of animal and plant plankton were added to sea water in glass vessels and the subsequent changes in the phosphate content of the water were followed.

The breakdown of the zooplankton was very rapid and more phosphate was set free than had originally been added as plankton. The balance was produced from dissolved organic phosphorus compounds in the water. The breakdown of phytoplankton showed a short time lag and only a part of the phosphorus added was set free as phosphate.

Although to many organisms manganese is known to be of great importance (Berkeley, 1922; Brenchley, 1927; Hopkins, 1930) its part in the economy of the sea is unknown. Some attempts were therefore made in 1934 to estimate the manganese in marine plankton using the residues from the determinations of phosphorus (Cooper, 1934; Harvey et alia, 1935). The residues from the triplicate digests from each cruise were combined and concentrated from about 200 to 70 ml. The concentrates were then examined quantitatively for manganese by the periodate method of Willard and Greathouse as described by Yoe (1928). In all cases but one the concentration of manganese was less than could be detected with certainty (Table I). In the absence of confirmatory data the figure of 5γ per litre of the diatom catch of May 15th must be regarded as suspect and attributable to chance contamination. Thus in these catches at L4 (5 miles off shore) during the spring outburst in 1934 manganese amounted to less than three parts per million million parts of water filtered, equivalent to one-thousandth or less of the phosphorus content.

The salt-marsh under investigation is situated at Aberlady Bay on the south shore of the Firth of Forth, fifteen miles east of Edinburgh.

The marsh is small and occurs at the mouth of a stream. The character of the soil on the two banks differs, being on the one side muddy with permanent pools, and on the other sandy, so that the pools tend to drain dry. The vegetation of the pools is variable, some containing species of Zostera, Ulva, Enteromorpha and Vaucheria, others having only diatoms.

1. The relation between the dry weight of the decalcified barnacle and its shell volume has been determined in its relation to age, season and tidal level, at Port Erin, with the following results: (a) In immature barnacles, tissue growth continues throughout the year, but is most rapid in the spring and autumn, (b) In mature barnacles which produce a considerable amount of larvæ there is a heavy drop in tissue weight during the summer period of high temperature, and another slighter drop during the winter, the latter being apparently associated with the presence of developing larvæ in the mantle cavity.

2. Gonad samples were examined seasonally. At low levels on the shore the barnacles mature in their first year. Above this level they do not commence to mature until over a year old. The sequence of changes in the gonads is described. A condition of senility is found in many of the largest high-water barnacles.

3. The naupliar content was estimated in relation to size and tidal level, counts of up to 13,000 larvæ per individual being obtained. The dry weight of a fully developed nauplius was determined to be 7·5×10-4 mgm.

1. Vertical traverses down the shore were worked at four localities in the Isle of Man, with varying degrees of wave-exposure, for which factor a coefficient is given.

2. The upper limit of distribution is high water neaps in a sheltered place, and up to high water of extreme spring tides at greater waveexposure. The lower limit similarly drops with increasing exposure.

3. Barnacles are largest and most abundant in a wave-exposed locality. The effect of wave-exposure may be reproduced by a current.

4. In sheltered localities the optimum level for growth, mean size, etc., is at low water for newly settled barnacles, but moves progressively up to high water as they grow older. In a very exposed situation, however, the optimum is always at low water.

5. In an exposed situation the gonads mature in their first year below about half-tide level, and in their second year above this level. With decreased wave-exposure the age of maturation rises, especially at high water until in a very sheltered place few barnacles mature at all.

The possibility that certain plankton organisms retained by a stramin net may prove of value as indicators in elucidating the water movements at the mouth of the English Channel is shown.

The water populated by Sagitta setosa is shown to be clearly demarked from that in which S. elegans lives, the latter living to the west of the Channel mouth south of Ireland. The water in which S. elegans lives has here been called “western” water.

It is shown that the planktonic indicators for “western” water are Sagitta elegans, Sagitta serratodentata, Aglantha rosea, Stephanomia bijuga, Clione limacina, Meganyctiphanes norvegica, Thysanoessa inermis, and Cosmetira pilosella (in spring and summer only). Sagitta setosa is regarded as an indicator of “Channel” water. Muggiæa, Salps, Doliolids, Liriope exigua and Euchœa hebes are regarded as indicators of “south-western” water.

The geographical distribution of S. setosa is discussed. It is shown that it is probably a neritic species mainly confined to the English Channel and North Sea.

S. setosa predominates off Plymouth when the easterly element in the Dover Straits current is suppressed and the flow of Atlantic water into the North Sea from the north is strong (Carruthers' Theory). The two Sagitta populations swing to and fro off Plymouth so that, with a strong flow of Atlantic water into the North Sea from the north, the S. elegans population is pushed westward to the mouth of the Channel and S. setosa occurs off Plymouth.

During the course of the five years, 1930 to 1934, an agreement has been found between the occurrence or absence of concentrations of the diatom Rhizosolenia styliformis in the southern North Sea and the variations in the composition of the Sagitta population off Plymouth In the years in which Ehizosolenia, an indicator of Atlantic water, was abundant in the southern North Sea S. setosa predominated off Plymouth; when Rhizosolenia was absent S. elegans predominated.

These diatom concentrations have been shown by Savage and Hardy t o have an apparent influence on the movements of the Herring which is reflected in the landings at Yarmouth and Lowestoft.

1. The general structure of the statocyst and the combined sensory setae in Honiarus vulgaris have been described.

2. The statoliths consist of sand grains attached to the setæ by a hyaline secretion.

3. Numerous tegumental glands occur in the sub-epithelial tissues. Though not situated beneath the setæ, their distribution varies in accordance with that of the setae. Their ducts have characteristic funnel-shaped endings, opening into the cavity of the statocyst.

4. The hyaline secretion agrees in all its reactions with the cuticle, never with the chitin.

5. The conclusion is reached that the hyaline secretion is formed by these tegumental glands and that this constitutes an important accessory function of these glands.

This paper embodies various observations which were made from time to time while the author was a member of the staff of the Plymouth Laboratory. It also outlines certain generalisations based on the author’s previous published work and that of other recent workers in the field of comparative physiology of feeding and digestion.

It has been shown (1, 2) that the capacity for building up visual conditioned responses is common to many types of fish when the unconditioned stimulus used as the basis for the “conditioning” is food. Preliminary work at Plymouth, using the fish Blennius gattorugine, showed that was possible that a knowledge of wave-length discrimination in that species might be acquired by the now familiar method of “conditioning” to an electric shock. This work was continued when I came to Cullercoats, and six specimens were used which were sent from Plymouth in 1929. All of these died within a short space of time during the succeeding winter months, owing to the intense cold. It was therefore necessary to restrict the investigation to Blennius pholis L., which is both plentiful and hardy at Cullercoats. Some progress had already been made and in Part II (2) it was intimated that an analysis would be made of the capacity for wavelength discrimination in Blennius pholis using an electric shock as the unconditioned stimulus. The present paper gives the results of that enquiry as far as it was taken.

Normal behaviour traits control the ability of fishes to form conditioned motor responses. This is shown by a series of experiments upon various species of fish in which it is found that Pleuronectids are found incapable of forming such responses for at least 200 associated presentations whilst other fishes have done so in less than 40. The bearing of the results on current theories of animal learning is briefly discussed.

In tow-nettings from Plymouth Sound, June 20th, 1935, Acartia clausi were abundant and inside these copepods, emerging from them and free in the water were very large numbers of larval trematodes, easily identified as Hemiurus communis. This is not a new record, for this parasite has already been described from the same Copepod in Plymouth waters in May and February (Lebour, 1923), but it has always been rare. In no case have more than two parasitised specimens been seen from these regions, and no seasonal appearance has been noticed. Much has been written about these trematodes which grow in the bodies of copepods until they are of such a large size that they inevitably kill the host and just before it dies emerge from between the joints, if not eaten before this with the copepod, but I think this is the first time that they have been recorded in any quantity at one time. Since my first communication Steuer (1928) has written about the geographical distribution of these hemiurids parasitising copepods and is of the opinion that all those in Northern seas belong to Hemiurus lühei and H. communis. In the Mediterranean the hemiurids known have not yet been found in copepods but usually in Sagitta, or are found living freely in the sea and these probably belong to H. rugosus which lives in the adult state in the pilchard.

Littorina (Melarhaphe) neritoides (Montagu) is stated by Tattersall to be viviparous. Living usually above high-water mark, often with Littorina saxatilis (L. rudis in Plymouth Marine Fauna 1931, Marine Biological Association), it would seem at first sight that free-swimming larvæ would be useless. L. saxatilis is truly viviparous and provided with a special pouch for its young which crawl out as small individuals similar to the parent. Tattersall (1908, 1909, 1920) when he discovered the planktonic egg-capsules of L. littorea (Caullery and Pelseneer (1910) having described them at almost exactly the same time) then regarded L. neritoides as viviparous. He has, however, kindly sent me the statement given below. Following him many workers have also declared that this species is viviparous (Flatteley and Walton, 1922, Colman 1933 Russell, 1934 and others). It is now possible to show that, not only is it not viviparous but it lays planktonic capsules very similar to those of L. littorea.

Attention was first drawn by Wilson (1932) to the large copepod fauna which can be found in an ordinary sandy beach. In his introduction he describes his method of collecting these copepods (p. 7) and in the course of the paper describes a number of new genera and species thus obtained.

Sand-dwelling animals, particularly Crustacea and worms (excluding sessile forms), are usually regarded as burrowers, since in their migrations they displace the particles of their environment. The fauna opened up by Wilson's discovery is of a quite different type. In contrast to true sand-burrowing animals, these copepods do not displace the particles of the sand through which they move but crawl over the surface of the grains, which, by capillarity, always hold more or less water, even high up on the beach at low tide. Such copepods, together with nematodes, rotifers, protozoa and other animals sufficiently small, may be regarded as part of an “interstitial” fauna.

Vertical hauls between surface and 45 metres depth were made with a measuring net, throughout 1934, at a position 5 miles S.W. of Plymouth Breakwater in circa 50 metres depth of water.

The phytoplankton organisms were counted and also assessed from their content of plant pigments.

A close relation was found between numbers of diatoms and their pigment contents after making allowance for the small size of three species.

The phosphorus content of the phytoplankton was estimated on several occasions.

The zooplankton organisms per cubic metre of sea were counted and estimations were made of their phosphorus content.

The diatom population differed from that found in 1933, in which year the spring outburst was shorter but more intense, the sporadic summer outbursts were more intense, the autumn one lasted longer; and more phosphate was utilised by the plants during the first half of the year.

A seasonal variation is found in the ovaries of immature hake (Merlucius merluccius L.).

There appears to be a seasonal change in the rate at which young eggs are formed from resting oocytes, as indicated (1) by the change in the relative abundance of nuclei in synapsis, and (2) by the change in the average diameter of the eggs in the egg-stock in the ovary. These processes show considerable correspondence in their season of incidence with the ovarian cycle of the mature and adolescent fish.

A physiological rhythm has now been detected in both somatic tissues and gonad in the immature hake, which foreshadows the physiological rhythm associated with the spawning cycle in the mature hake. The implication of this on the question of the formation of “growth-rings” in the skeletal structures is briefly discussed.