Determinations of phosphate, silicate, nitrate, nitrite and ammonia have been made at frequent intervals at two Stations, L4 and El, in the English Channel off Plymouth between the autumn of 1930 and January, 1932. Determinations were also made quarterly at E2 in mid-Channel.

The year 1931 was an early one from the point of view of plankton production. The chemical data show that there was a small mid-winter outburst which gathered momentum during January and February. The main spring outburst started, however, early in March, carrying on fairly steadily until about the middle of May. The summer was characterised by exceptionally low phosphate and nitrate right through the water column due to very efficient utilisation in the spring and to the unusual hydrodynamical conditions. There was also a small autumn outburst.

1. The limitations of the Conical Dredge as used in obtaining a sample for quantitative estimation of the fauna of a ground are discussed, and are found to be related to

(a) The great distance over which the instrument must be hauled, with consequent inability to detect patchiness of fauna.

(b) The inability of the dredge to capture members of the epifauna.

2. The nature of the shell gravel, its position relative to the Eddystone reef, and the various factors conditioning the degree of coarseness of the deposit and the segregation of its elements are considered. The main points of note are,

(a) There are three well-defined areas, within which the gravels have their own particular characteristics.

(1) The Inner Shell Gravel area and the Middle Gravel area, composed of material of inorganic and organic origin, the former being gneissic in character, and the latter being formed of the remains of animals which normally live on this particular type of deposit.

(2) The Outer Shell Gravel area, a mixture of matter of local and of outside origin. The area is more extensive on the western than on the eastern side of the reef.

(b) Segregation of particles according to size occurs, and is illustrated by the movement of the valves of a number of species of molluscs. Wave action and the action of gravity are considered to be the chief factors in inducing movement of particles, which movement occurs in directions radiating from the reef outwards.

3. The epifauna of the rocky bottom is referred to briefly.

4. The infauna of the shell gravel has been examined quantitatively and qualitatively, and the range of the various species over the ground noted.

5. The nature of the shell-gravel community and its relation to some of the important environmental factors, are discussed.

6. Mortality among the lamellibranchs, and the depredations of the gastropod Natica alderi are considered; figures relating to the numbers of lamellibranchs killed by N. alderi are given.

A survey of the sandy beach at Port Erin, Isle of Man, was made in. September, 1931. Observations were made, at a number of stations, involving simultaneous records of the macro-fauna and its density, and certain physical and chemical factors of the sand and interstitial water, as well as tidal level on the beach. The results enable certain general conclusions to be drawn as to the causes of the observed distribution of species, and of the differences between the faunas of this and some Scottish beaches. Plans are given, indicating tidal contours, salinity, and grade composition, in situ on the beach, together with frequency diagrams for five dominant species.

(1) In general, the changes in pH were similar to those observed in previous years. On six occasions the pH at the surface at Station L4 was lower than at the bottom.

(2) The changes in carbon dioxide in the spring agree with the conclusion, formed in Part I from nutrient salt data, that the early start in plant production in mid-Channel was not maintained and that by the middle of April production had become much greater nearer the shore.

(3) The partial pressure of CO2 during nine months out of twelve has been observed to be lower than that of the atmosphere and equal or slightly higher during the remaining three months.

(4) It is suggested that the fall in (Total CO2+O2) during the course of the summer was due mostly to loss of oxygen to the atmosphere. After allowing for carbon dioxide possibly removed from the sea as calcium carbonate and for the loss of oxygen due solely to rising temperature of the water, a net loss of 110 litres of oxygen was found from a column 1 sq. metre in cross-section and 70 metres deep; or 9 cubic kilometres from the whole of the Channel. If this is regarded as a closed system, the oxygen must have been formed during photosynthesis from an equal volume of CO2 dissolved from the atmosphere. But the required transfer of CO2 across the surface of the sea is too great to be accounted for by existing data on the rate of invasion of CO2 into sea-water as calculated for a small bubble of gas in water.

(5) Estimates of the phytoplankton crop have been made, based on the seasonal consumption of carbon dioxide, of phosphate and of nitrate and on the oxygen lost to the atmosphere. All four are of the order of 1,400 metric tons wet weight per sq. km. of surface, in close agreement with the figure calculated by Atkins. The crop production calculated from consumption of silicate is less than one-tenth of this. This is attributed not only to the presence of planktonic organisms requiring no silica but to the silicate being used several times over in the course of the season.

(6) About 0·06% of the wet weight of phytoplankton produced is harvested as fish.

(7) A small variation in excess base, equivalent to about 0-1% of the total calcium present, has been detected between the surface and bottom in summer. The result requires confirmation.

It has been shown by Eeid (1930) that the salinity of the water retained in a sandy foreshore at low tide may be considerably higher than that of a stream of brackish water flowing over it. A few similar observations have been made on the salinity of the water held in the muddy foreshore of the estuary of the River Tees.

The following is a continuation of the work described in a previous paper (Reid, 1930). The intention was to amplify that work by the investigation of the conditions of salinity interchange on sandy shores of less ideal type. It was considered likely that various factors might affect the condition of the water held by the sand. For instance, the rate of flow of the fresh water and its depth; irregularity in the slope of the beach; the depth of the sand and the nature of the floor on which it rests. The rate of flow of the water is not a simple factor however. It is correlated with the slope of the beach in that faster streams are usually on steeper beaches. The effect of this dual factor will be discussed later.

In a previous paper (9) attention was drawn to the occurrence of five different “Mutant Stocks” of ‘Red-eye’ deviations from the normal black eye. Various differences in the characteristics of these stocks were indicated. For instance, Stock I Red-eye is a stable Bright Red behaving as a simple mendelian recessive, whilst in Stock V all kinds of shades of eye-colour occur with various sorts of changes during life.

On each of two former occasions when specimens of Gammarus chevreuxi Sexton have been brought from the wild into an incubator and kept at 21° C. or more, red-eyed recessive types have been reared among the F2 progeny (4, pp. 190 and 194). In November, 1930, an opportunity occurred for making further tests on this point. Twenty-three wild pairs, taken in Chelson Meadows on November 19, were placed on the following day in the incubator, the temperature of which at first averaged between 21° and 22° C, but was raised after a few days to an average of between 22° and 24° C. The young which were extruded from eggs laid in the wild were discarded. Those of subsequent broods were reared with a view to obtaining as many F2 families in each stock as would give a reasonable opportunity for segregating recessive characters to appear. The F2 young were examined for recognisable variations that might indicate the presence of a recessive character.

A description has been given of a mating which produced a great range of eye-irregularity in the offspring. Not only were the size, shape, and pigmentation affected, but the eye-structure itself, many cases occurring in which one eye or even both eyes were missing at birth.

This experiment adds another proof to the statement that the farther removed from the normal an animal is, the lower its viability. The mortality was much higher amongst the abnormals, and breeding experiments with the survivors were exceedingly difficult on account of the trouble experienced not only in rearing them to maturity, but in finding suitable mates. The cannibalism of the males of this stock made it almost impossible to use them, and small, not too vigorous, males had to be sought in the Albino No-white strain.

In three of the One-eyes, i.e. those in which one eye was present at birth, and no trace of a second could be seen (even with a high power), a very imperfect second eye developed later, after several moults had taken place. An example, CN.220c, is illustrated in Text-fig. 5 (List, p. 384).