By the use of a “conditioned response” technique it has been shown that teleostean fishes respond “purposively” to an increase in temperature of the water surrounding them of between 0-03° C. and 0-10° C. It is probable that the former figure is true for all the species investigated, but it has only been practicable to establish it with certainty in a few sedentary forms

1. The diameters of samples of Rhizosolenia stylijormis taken in the S. W. North Sea between 1932 and 1934 revealed the presence of large and small populations. The largest diatoms were found in 1933, in which year, or late in 1932, it was thought that auxospore formation might have taken place.

2. The large and small groups mentioned in (1) gave indications of a continuous diminution of size judging by an inspection of their modes. Notwithstanding this there appears to have been some selection of the larger cells, as the whole samples tended to increase in size with a rise of temperature.

3. The correlation coefficient between the temperature at 20m. and the mean diameters was 0-59. That for salinity in the same circumstances was 0-59. The inverse correlation with salinity is thought to be due to the topography of the area.

By examination of samples of Purpura lapillus from the whole of their European range, it appears that the species can exhibit quite as wide variation within a relatively small region such as that studied in the Dorset-Devon-Cornwall area, as it can over its whole geographic range. Population samples were taken from seventy-six localities, mostly in the south-west of England, and covering a wide range of environmental conditions, and the variations in these shells were studied in relation to two primary environmental factors, degree of exposure to wave-action and diet.

Several small anemones resembling Metridium dianthus were collected from the River Roach and sent to me in the summer of 1934. A careful examination proved them to be Diadumene cincta which was first recorded from Plymouth. T. A. Stephenson (1, 1925, p. 880) described both an orange and a fawn variety of this species, the former from the Breakwater and the latter from the Pier, Plymouth. The Roach anemone agrees with the Plymouth one in all its more important habits and its external and internal characters. It would appear that the specimens of D. cincta from the New England Creek, Essex, recorded by T. A. Stephenson (2, 1935) since this account was first written, may have been derived from this river.

The anemones were dredged in abundance from the River Roach attached to living and dead shells of Ostrea and Mytilus and to Alcyonidium and Halichondria. All (about thirty) which I have seen were small, the diameter of the base averaging 0.6 cm. and the disc 1.5 cm. They were orange, but some were pale while others were more deeply coloured. No fawn ones have as yet been found in this locality.

The scapus wall is thin, translucent with a bluish caste and with the mesenterial insertions showing through. The cinclides are evident as distinct dull purple-grey spots, each with a central depression clearly visible under a hand lens. The tentacles are the same colour but paler than the scapus. They are usually uniformly coloured but in some specimens there are two faint bluish lines running along their upper surface and, in one individual, there was a pair of short dashes at their bases instead of these lines.

This list contains 2 species of Tanaidacea, 6 of Isopoda and 28 of Amphipoda. These were all collected by myself in 1934–5, with the exception of 3 species of Amphipoda, which have not been entered in the Plymouth list although accounts of their capture at Plymouth have been published. These are Eusirus longipes Boeck, recorded by Hunt (1924); Gammarellus angulosus (Fabr.), by Kitching, Macan and Gilson (1934); and Gammarus zaddachi Sexton, by Serventy (1935).

The list is drawn up in the systematic order adopted in Plymouth Marine Fauna (1931), with a reference to a good illustration of each species. The dates and circumstances of capture are stated, and when a species has already been recorded from off the coasts of Devon and Cornwall by Norman and Scott (1906) a note to that effect has been made. The distribution is not stated, since recent accounts of the distribution of every species are available in the following works:

Tanaidacea and Isopoda: Nierstrasz and Stekhoven, 1930 (except for Synisoma acuminatana, q.v.).

Amphipoda: Chevreux and Fage (1925) or Stephensen (1929).

All the Amphipod species in this list are included in one or other of these publications, and almost all in both.

Every species has been referred to a specialist for identification. Tanaidacea and Eurydice truncata and Gnathia oxyurœa to J. H. Schuurmans Stekhoven of Utrecht; the other Isopoda to Prof. W. M. Tattersall of Cardiff; the Amphipoda to Dr. K. Stephensen of Copenhagen, excepting Gammarus zaddachi Sexton, which Mrs. Sexton herself has named.

Descriptions of the hydroid Zanclea implexa (Alder) in British waters have been given by the following authors, Alder (1857, as Tubularia implexa and Coryne pelagica), Allman (1859, as Coryne Briareus), Strethill Wright (1859) and Alder (1862 as Coryne implexa), Allman (1864 as Zanclea implexa and 1872 as Gemmaria implexa) and Hincks (1872, as Zanclea (Gemmaria) implexa). All these descriptions have been based upon full grown colonies in which the hydranths had a perisarc on the hydrocaulus.

In the last number of this Journal (Russell, 1936) I described under the name Eucheilota hartlaubi the adult and various stages of a medusa that is fairly common in the Plymouth plankton but had up till then remained undescribed. This medusa was identified with an unnamed medusa which Hartlaub had figured as having been reared from the hydroid Lovénella clausa Lovén.

On March 10th, 1936, some Lovénella clausa kept in this laboratory by Mr. W. J. Rees liberated medusæ. Mr. Rees kindly handed these over to me so that I could follow the early development. When first liberated the medusa was conically bell-shaped (Fig. 1) and there were scattered nematocysts on the exumbrella. There were two fully developed opposite perradialtentacles, and two non-tentacular perradial bulbs. Rudiments of spiral cirri were developing on either side of the tentacular bulbs. There were four interradial marginal cirri each of which was situated on the umbrella margin about midway between the tentacular and nontentacular bulbs.On the tentacle sides of each of these marginal cirri was a marginal vesicle with a single concretion. The medusa was 0.75 mm. high by 0.75 mm. broad. The colour of the tentacular and non-tentacular bulbs and the stomach was pale straw. By the next day the umbrella had assumed amore oval bell-shape and the colour of the bulbs and stomach was now a bright orange-yellow. OnMarch 12th the medusa was now 0.9 mm. high and the rudiments of cirri were developing on one side of each non-tentacular bulb (Fig. 2).

The writer has recently reared a species of hydroid at Plymouth, which, in the vegetative state, might easily be confused with Slauridium productum Wright, 1858. The original creeping stolon from which the colony developed was found on a piece of dead Eunicella verrucosa (Pallas) dredged by the S.S.Salpa near Stoke Point on March 9th, 1936.

When isolated in a finger-bowl with “outside” sea water the stolon bore no polyps and showed no sign of activity, but three weeks later a single polyp had developed (Fig. 3). From its close resemblance to the figures given by Hartlaub (1895) for S. productum, it was at first assumed to be this species and was carefully watched and fed in the hope of rearing the medusæ from it. After a period of time, however, when the colony had increased considerably in size, styloid gonophores were developed.

The type of growth of the fully grown colony is shown in Figures 1 and 2. The stems are elongated and slender, bearing polyps at intervals. Polyps are borne at the summit and also on branches of the main stems. These branches usually arise from one side only of the main stems and it is probable that under natural conditions in the sea these main stems are really stolons. It is also likely that in nature the intervals between the polyps are fairly short. The whole colony has a faint yellow-brown colour which becomes reddish-brown in the polyps and the upper part of the hydrocaulus.

A troublesome problem arises in connexion with the tracing of Trematode life histories; namely how to obtain the intermediate and final hosts free from Helminth infections. It was discovered—fortunately early— during the study of the parasites of Peringia ulvœ Pennant 1777, that all the species of certain groups of cercariæ, and also related species from other molluscan hosts, encyst most readily in the same species of fish or crab. It is therefore not surprising if the mature trematodes are also to be found in the same host. It is obvious that the greatest confusion can arise from these facts. To add to the difficulty it is often impossible to distinguish between the worms within the cyst, and therefore the dissecting out of cysts for feeding purposes is impracticable.

By far the most satisfactory results are obtained by rearing the hosts in the Laboratory, but unfortunately with marine organisms this is often impossible.

The Black-headed Gull was selected as the final host in a series of experiments, approximately 40 Helminth parasites having been recovered from this bird in Europe. Attempts were made to rear the bird in captivity.

Two dozen eggs were first placed under various hens, but all those were lost owing to the great fragility of the shells. The birds invariably smashed the eggs in turning them. An incubator was then tried but a large series of failures also occurred before the discovery of the correct temperature. Subsequently half the birds died on account of wrong treatment after hatching.

A number of naturalists have expressed their belief that the movements of the adult herring (Clupea harengus L.) at certain seasons are governed by the relative abundance or scarcity of their food or other organisms in the plankton.

The English fisheries which were investigated with the Plankton Indicator in 1931,1932, and 1933 were divided into three areas, i.e., those off Shields, the Humber mouth and the East Anglian coast (this last fishery was also sampled in 1930). All the samples in the Shields area lie between 56° 00 N. Lat. and 54° 20 N. Lat., whilst the majority (80%) lie in the area between 54° 45 N. Lat., and 55° 30 N. Lat. and a line parallel to and some 40 miles from the coast. This is an area of some 1600 square miles. In the Southern Bight Lat. 53° 00 N. was taken as a division between the Humber and the East Anglian areas. The distribution of all the samples is shown in Figs. 1 to 4. With the exception of the samples obtained by the Ministry of Fisheries research ship Onaway in June, 1931, and four samples obtained by H.M.S. Chenoell in September, 1933, all those in the Shields area have been collected by individual drifters engaged in the fishery. The Humber and East Anglian samples were obtained from both drifters and gunboats of the Fishery Protection and Mine Sweeping Flotilla alongside drifters fishing. The manner of collecting these samples has been described in Part I (p. 153).

(1) In the Scottish Eastern and Western Fisheries 459 Plankton Indicator samples have been analysed and the results studied for evidence of correlations between the zooplankton and the 533 associated catches of herring. (See Part IV for the phytoplankton correlations.)

(2) In the Eastern Fishery, 1930-33, out of twenty half-month areaperiods considered of primary value, fifteen show positive Calanus-Herring correlations and five negative. The area-periods of secondary value confirm this three to one ratio, there being eight positive and three negative results indicated. (A three to one ratio was also found in the Shields Fishery. Part II.)

(3) An attempt to estimate the commercial value of the Indicator, when used to locate the richer Calanus waters, shows that if in each period (1931-33) the fishing had taken place in the richer Calanus waters a gain of 24-5 i 7 -7 % over the catch secured by fishing at random should have resulted.

The object of these investigations, discussed in full in Part I, is an attempt to correlate the catches of the drift-net herring fishery with the conditions in the plankton at the time of fishing, and if possible to establish useful indications as to suitable and unsuitable waters for fishing. In Parts II and III the zooplankton-herring correlations in the English and Scottish fisheries have been dealt with separately. The phytoplankton material with which this section deals is not so extensive, so that the data from both fisheries will be dealt with together. The pioneer observations of Pearcey (1885) in regard to the herring, of Bullen (1908) inregard to the mackerel, and the fact that fishermen have for long regarded what they call “weedy” or “stinking” water as a bad sign for fishing, have been referred to in Part I, page 148.

Investigations into the relations between plankton and herring, using the Hardy Plankton Indicator, were carried out by this department during the years 1930 to 1933 (Hardy, Henderson, Lucas and Fraser, 1936). In planning this work Professor Hardy made provision for obtaininginformation, when possible, on weather conditions and on the occurrence of organisms which would not be caught in the plankton samples. Information on the presence of jelly-fish, was specifically requested. Skippers of drifters using the Indicator were asked to fill in a printed labelfor each disc giving details of ship, date, time, position and catch, and the following sentence was printed at the foot of the label:— “ Any further notes regarding state ofweather, sea, presence of jelly-fish, or any unusual conditions may be written on the back.” Since the details of date, position, catch, etc., were essential for the success of the Indicator experiments, only these were definitely asked for, and skippers were left to supply further information if they had time to do so. Much more exact and extensive information regarding the presence of jelly-fish arid other organisms could have been obtained if the enquiry had been confined to these points, and it is hoped that this may be done in the future, either from thisdepartment or by other workers. Russell (1935, b), in stressing the importance of plankton organisms as indicators of different hydrological conditions, says “it is especially valuableto watch for any correlations between the presence or absence of certain plankton animals with that of fish and larger swimming animals.”

Trochosphekes of Nephthys hombergi Lamarck are readily obtainable at Plymouth when the adult worms are mature from June to September. The worms are dug out of the muddy sand on the lower regions of the shore, and their eggs and sperms obtained by slitting open the body cavity. Fertilizations are easily made in glass finger-bowls of clean sea-water. Although apparently ripe worms have been kept under sea-water circulation in the laboratory, and under a variety of conditions, none has ever been induced to spawn naturally. After some days the body walls of some individuals have split along the back and shed their genital products in that way; these, however, were probably unhealthy and abnormal. A high percentage of the eggs got by cutting open the worms have fertilized and given rise to cultures of strongly swimming larvæ. During the summers of 1932–34 much time and effort were expended in numerous attempts to rear these larvæ, but in no single instance was success obtained. It had been hoped to collect material for a detailed histological study of the development, for it may be of a straightforward and simple type that would throw light on various problems of Polychæte embryology. Although these hopes have not been realized it seems of value to describe the trochosphere of which no entirely satisfactory account exists, in spite of a few references to it by previous writers.

Accounts of the ovarian development of the eggs of fishes have been given by Kisselevitch (1923). Mayenne (1927), and recently by Hickling (1930) and Raitt (1933). They have concluded that in the ovary of the adult fish there is a general egg-stock of small eggs, yolkless and transparent in fresh material, and with deeply staining cytoplasm in fixed and stained material. From this egg-stock a quota is withdrawn each year to be matured and finally spawned, and to this egg-stock a fresh batch is added each year by the development of oocytes present beneath the surface of the ovigerous lamellæ, the minimum period of development being two seasons.

It has occurred to us that measurements of the diameters of eggs, in ovaries well advanced towards spawning, may give evidence of the duration of spawning in a fish of which the spawning habits are unknown. For where the spawning period is short and definite, the batch of transparent yolkless small eggs, destined to mature and be spawned, will be withdrawn from the general egg-stock in a single group, sharply distinguishable, at least in the later stages of maturation, from the stock of small eggs from which it was derived. But when the spawning period is long and indefinite, the withdrawal of eggs from the egg-stock, to undergo maturation, will be a continuous process, and there will be no sharp separation between the general egg-stock and the maturing eggs. These will pass continuously one into the other. We have tested this hypothesis with four species of fish of known spawning habits.

During the progress of the work on Gammarus chevreuzi it became increasingly evident that heterozygosity must exist in the wild population.

The work began in June, 1912, simply as a study of the life-history of some of our common amphipods. The genus Gammarus was chosen, because of the number and the wide distribution of its species in the neighbourhood. Seven of these species, all black-eyed, from marine, estuarine, brackish and fresh waters, were kept in the laboratory for investigation until the first red-eyed specimens were discovered in one of the brackish species, later described as Gammarus chevreuxi (see p. 360). Since the manner in which these red-eyed individuals occurred raised points of considerable interest, it was decided to confine investigation to G. chevreuxi, and a series of experiments was started. The different variations involving both the structure and the pigmentation of the body and of the eyes appeared from time to time, some behaving as simple mendelian characters and attributable to the presence of a single recessive gene, others with a more problematical hereditary basis. These variations have been recorded as they occurred (see bibliography). For ten years, no second mutation appeared, although frequent dredgings were made and the animals thus obtained were kept for several generations in laboratory conditions. Because of this apparent stability of character the wild Gammarus was regarded as a homogeneous population until, in 1922, it became increasingly evident that the results showing in the laboratory cultures could only be explained on the supposition that many recessive factors must be present in the natural conditions.

The evidence steadily accumulated, but direct proof was very difficult to obtain partly because (as we found in our experience with the cultures) the recessive types are often less viable than the normal, and therefore probably less able to withstand the competition in the wild, and partly perhaps because we had no criteria by which to assess the influence of the laboratory conditions (changes of temperature, food, salinity, pressure, etc.) on the constitution of the Gammarus, and so could not decide whether a variation was caused by the inherent action of the recessive genes, or by the untoward environment producing a change in the action of the normal genes.