The rapid growth of bacteria when sea water is stored in glass vessels, and the possibility that this is brought about by the concentration of food by adsorption on the solid surface, are discussed. Some evidence is presented bearing upon such adsorption.

The regeneration of phosphate from dissolved organic phosphorus compounds in the sea and in stored water is considered.

In a previous paper (Smith, 1940b) the chemical changes observed in ocean sea water flowing across the shallow banks on the west coast of Andros Island (Bahamas) were reported. High salinities were produced by evaporation and calcium carbonate was precipitated. From the data obtained under natural conditions a maximum value of the solubility product constant of calcium carbonate in sea water was suggested. There was no reason to believe, however, that this value of the constant represented the true equilibrium conditions, and experiments have since been made in the laboratory with a view to bringing water from these banks into equilibrium with solid calcium carbonate.

It is shown that the average number of embryos produced by a gravid oyster is approximately doubled each year until the oyster is 4 years old, when it may be regarded as adult. Estimates have been made of the quantities of embryos produced by one 1-year-old, eleven 2-year-old, fourteen 3-year-old and twenty-two adult oysters; the mean values for these year-classes are 91,600, 218,100, 462,600 and 902,900 respectively.

Since it is probable that the proportion of a population of oysters which matures in the female phase increases progressively up to the age of 4 years, it follows that adult oysters are for this reason superior to 2- or 3-year-old oysters as breeding stock, quite apart from the increased number of embryos produced by each oyster.

1. Measurements of Carcinus, comparable to those taken by Weldon at Plymouth 40 years ago, have been made on material from three Irish localities, the observations in each area extending over three years. The three localities afford different environments, one having no silt, one a moderate amount and the other much silt.

2. The results support the view that the change in the ratio frontal width/ carapace length with increase in body size is due to differential growth in the individual and is not caused, as Weldon supposed, by the continuous removal through natural selection of those crabs with a relatively wide frontal aperture. Measurement on the growth of individuals confirms this view.

3. A striking fact which emerged from Weldon's work was that the ratio mentioned above showed a successive diminution in each of the three years covered by the observations. A precisely similar diminution has been found at each of the Irish localities, and it is shown that the annual differences are mathematically significant.

4. The results disprove Weldon's hypothesis that the change in the ratio is correlated with the slow accumulation of silt in Plymouth Sound. The Irish locality with most silt has the widest frontal aperture and the intermediate locality the narrowest. It is also shown that the yearly trend towards a lower value for the ratio cannot be continuous, for the rate of change is too rapid to be maintained indefinitely, and the values obtained in the Irish localities overlap those at Plymouth 40 years earlier. Possible explanations of the changes are discussed.

5. The differences between populations from the three localities in any year are much less marked than the annual differences at one locality, and are not generally significant. Though small, however, they do show a consistent sequence among the three localities (but not corresponding to the order for siltiness).

1. S. horsti occurs on the Hampshire coast of the Solent near the mouth of the Lymington River, in glutinous grey mud associated with Corophium volutator.

2. The species is distinguished by the following characters: coloration; dorsal and ventral grooves present on the proboscis throughout its length; collar forming a slight operculum posteriorly; ventral muscle bands of the trunk forming projecting ridges; rounded genital ridges present, the gonads beginning within 1 mm. of the collar; 100–140 pairs of gill slits; longitudinal muscle fibres of the proboscis arranged in nine or more concentric rings; ventral septum of the proboscis short; stomochord straight, with ventral diverticulum and wide lumen throughout; no dorsal glomerulus present; single proboscis pore on the left side; proboscis skeleton embracing half to two-thirds of the circumference of the buccal cavity and extending one-fourth to one-third of the length of the collar; four epidermal zones present in the collar; collar cavities completely separated; anterior extensions of the collar cavities extending into the neck of the proboscis; perihaemal cavities separate posteriorly but confluent in front of the level of the tips of the crura, and extending into the neck of the proboscis as far as the proboscis pore; neural keel well developed and in continuity with the epidermal nerve layer at intervals; no dorsal diverticulum of the buccal cavity; branchial epidermis characterized by the predominant intensely eosinophil glandular elements; tongues broader and projecting further into the lumen of the pharynx than the septa; epibranchial ridge formed by two convex ridges bounding a median groove; oesophagus divided into three regions; 4–8 intestinal pores; hepatic region of gut not sacculated and with an expanded lumen; gonads not lobed; oocytes attain a size of 0·23 × 0·17 mm.; yolk cells present in the ovaries.

3. The probable identity of the specimen of Saccoglossus from the French coast of the English Channel, recorded by Caullery & Mesnil (1916) as S. kowalevskyi, with this species is discussed.

The male of Haustorius arenarius is identical with the female in all external morphological characters apart from the absence of brood lamellae. The females develop brood lamellae at 5 mm. total length, eggs appear in the brood pouch at 11 mm., and they may reach a length of 14 mm. The largest male obtained measured 10 mm.

It has been shown in a recent paper by Russell (1940) that in addition to Podocoryne cornea M. Sars, 1846, and the so-called P. areolata, two other Podocoryne medusae, viz. P. hartlaubi Neppi & Stiasny, 1913, and P. minima (Trinci), also occur in the plankton in British waters. The identity of both hydroid and medusa of the European P. cornea is well established arid the medusa has never been known to mature with more than 8 tentacles (Kramp, 1927; Russell, 1940). P. minima is a small medusa with only 4 tentacles and need not be considered further in this paper.

1. The brackish-water prawn Palaemonetes varians and the marine prawns Leander serratus and L. squilla are hypotonic in normal sea water, the blood of these species showing osmotic pressures equivalent to 2·3, 2·8 and 2·6 % NaCl respectively, in an external medium of 3·5 % NaCl.

2. Palaemonetes varians is isotonic in water of about 2·0 % NaCl and the species is practically homoiosmotic, the difference in its osmotic pressure over a range of 5·0 % NaCl in the external medium being only 0·8–1·0 %. The species has a very wide range of tolerance from water that is nearly fresh to concentrated sea water equivalent to 5·2 % NaCl.

3. Leander serratus is much less homoiosmotic than Palaemonetes, and has a limited tolerance to dilution and concentration of the environment. Homoiosmoticity is maintained up to a dilution of 2·5 % in the external medium when isotonicity is reached; but in lower dilutions there is a steady decline in osmotic pressure and the regulatory mechanism evidently breaks down.

4. The osmotic behaviour of Leander squilla is very similar to that of L. serratus, but the homoiosmotic behaviour is more marked and it has greater tolerance to dilution of the environment.

5. When Leander and Palaemonetes are transferred to very dilute sea water, the internal osmotic pressure falls gradually for about 14–24 hr., varying according to the size of the individual. After the lowest value has been registered there is a slight rise, and a steady state is thereafter maintained.

6. Studies on the changes of weight of prawns when transferred to diluted media indicate that the integument (gills) is permeable to water and that, at least in Leander serratus, the amount of water entering is mainly responsible for the dilution of the blood. There is a similar fall in weight when prawns are transferred to concentrated media, due to loss of water.

The migratory habits of Gadus merlangus and G. pollachius are examined n i relation to the variations in the rate of infection of these fish with Lernaeocera branchialis. A sudden increase in infection in estuarine and inshore waters is found to coincide with the offshore migration of the main stock. The infected fish apparently linger behind and may live for some time in the old habitats after the arrival of the next recruitment. The offshore migrants are seldom infected, and it is probable that infection does not take place in water deeper than about 5 fathoms.

The possible immediate causes of this “lingering” phenomenon are examined, and two suggestions are made as to the nature of the physiological upset brought about by the presence of L. branchialis on these gadoids. Other factors influencing the distribution of the parasite are discussed.

The relative susceptibility of the different species of gadoids to infection with species of Lernaeocera is examined as far as the data allow.

A study of the distribution of Trebius caudatus from four species of Raja trawled from two localities of different depths at Plymouth shows that there is a higher infection rate in the deeper water.

Both at Roscoff (France) and at Plymouth the mean total rate of infection is about 20%, and the larger fish are more often infected than the smaller. Both sexes are equally parasitized and the copepods tend to collect near orifices on both surfaces of the fish (regions where the mucus secretion is maximum). Immature forms were found at Roscoff in the mucus of the orifices themselves. The collections from both places contained about equal numbers of male and female parasites.

Intestinal respiration, a feature common to free living and parasiticcopepods, includes the gaseous exchange through the gut wall, the associated movements stirring the oxygen vector (which is either the external medium taken in by the anus, or the food current when this is the blood of the host), and the circulation of the body fluid as a direct result of these movements. The significance of the gut movements, which include the peculiar two-way peristalsis, is examined in detail in Trebius caudatus and Lernaeocera branchialis: the former has a functional anus which admits the external medium and the latter has a closed anus and employs the blood of the host as the oxygen vector.

The old type of wire-angle indicator, which consisted of a pendulum swinging across an arc of a circle graduated in degrees, and which had to be applied by hand to the wire, was clumsy to use, especially in bad weather, and when the wire led out over the stern of the ship. It needed someone to attend to it, which often resulted in the wire angle not being checked more than once every five or ten minutes when the crew were busy. This instrument was therefore designed to remain in place throughout the tow, and to give a large dial reading which could be easily seen from a distance. On the research ketch Culver there is an engine throttle control mounted close to the wheel, and all the man there has to do is to adjust the engine speed so that the large indicator in the instrument remains on the red line. In practice it was found that the wire angle rarely varied more than about ±2°, except in very bad weather, and so the depth of the nets could be regulated very closely. The instrument is oil damped, so that the pitching of the ship and the vibration of the wire during hauling do not affect it. It has been used for about two years on the Culver at Bermuda; it has needed no attention in that time, and, which is a good point, the crew like using it.