Between March 1933 and June 19391 a series of vertical hauls with a plankton net has been made at a line of six stations 12 miles apart, the first lying off Flamborough Head and the last on the south-west patch of the Dogger Bank. This line was usually visited at monthly intervals, the net used being of the Hensen type fitted with bolting silk of 60 meshes to the inch and hauled to the surface by the counter-weight device introduced by Buchanan-Wollaston (1911). Hensen (1887) worked out a filtration coefficient for his net, and when this was applied to the dimensions of the one in use and the depth through which the vertical hauls were made, it was possible to express the catch in numbers per cubic metre of sea water. It was also possible to give the individual catches by weight, and it may not be without interest to observe, before passing on to deal with numbers, that the dry weights taken in 1936 varied between 0.2600 g. per m.3 in August and 0.0015 in February.

Although the net method of estimating plankton has often been decried as unreliable, Hensen net results have always given a consistent picture of relative plankton densities in the North Sea. Confidence arising from this consistency has not been lessened by a comparison of the net and sedimentation methods which has been made in respect of the May 1938 samples.

The sedimentation method consists in counting the entire deposit of microplankton which has settled on the floor of a glass cell containing a known volume of sea water.

Two species of Portumnus occur in the Plymouth area, P. biguttatus (Risso) and P. latipes (Pennant). P. biguttatus was the only species recorded when the old fauna list of Plymouth was published (1904), but since then it is known that P. latipes is very common in certain sandy areas (see Plymouth Marine Fauna, 1931), far commoner than P. biguttatus.

P. biguttatus is rare and has not been seen since 1906. It was first found by W. Garstang and R. Todd on Drake's Island in Plymouth Sound, burrowing in fine gravel (1905), and two specimens, and are recorded from a sandy patch from the north-east corner of Drake's Island. A female in berry was recorded from the same locality by R. Todd, and L. R. Crawshay dredged one in Cawsand Bay in 1906. Apparently the eggs were not hatched out and the zoea of this species is unknown. In August 1902 R. Gurney obtained a megalopa in the plankton and from it secured the first crab stage. He describes the megalopa as being intensely blue. The cast skin of the megalopa and the crab obtained from it (Fig. 3a-c), which he kindly handed to me, are described in my paper of 1928 (Lebour, 1928c, p. 518, pl. viii, figs. 1–3). There is no reason to doubt the accuracy of the determination, especially because, as shown below, corresponding stages of P. latipes as well as the zoeae are now known and are very distinct, differing considerably from those of P. biguttatus.

Spadella cephaloptera

1. The oesophageal epithelium is composed of granular and vacuolated cells. The former produce a glutinous secretion which appears to immobilize and lubricate the prey. The function of the vacuolated cells remains undetermined.

2. The intestinal epithelium is composed of gland cells and absorptive cells. The gland cells contain large vacuoles which disrupt when food is taken, restitution taking several hours. The absorptive cells accumulate large concretions of fat and other material as digestion proceeds; later this gradually disappears.

3. The absorptive cells in the intestine are ciliated. The cilia may be concerned with respiration and excretion; there is no evidence that they are concerned with osmoregulation.

4. The rectum has a ciliated columnar epithelium.

5. The general course of feeding and digestion,is discussed.

6. It is stated in a footnote that the reproductive system of Spadella is similar to that of Sagitta.

Sagitta setosa

7. The oesophagus is divided histologically as follows: (i) a region of granular cells round the mouth; (ii) a region of vacuolated cells; (iii) a region of compound granular cells; (iv) a second region of granular cells. The granular cells produce a profuse secretion with probably the same function as the glutinous secretion in Spadella.

8. The intestinal epithelium is composed of compound granular cells and simple columnar cells. By comparison with the intestine of Spadella the former are regarded as enzyme-secreting cells and the latter as absorptive.

Previous methods of survey by American workers are described and the differences between the species of seaweed involved are emphasized. The small stature of the European kelps renders all methods of survey difficult and the results can only be described as the best approximations. The British survey was divided into (1) a preliminary survey in order to determine the regions with the biggest beds, and (2) a detailed survey, when some of these major beds were mapped in detail. The primary survey was a rapid affair and the results were based on information obtained from (a) use of boat and grapnel, (b) existence of cast weed, (c) lobster fishermen, (d) coastguards, fishery officers, borough surveyors, harbour-masters, (e) inspection from cliffs, (f) a study of Admiralty Charts.

In the section on the detailed survey the different types of grapnel employed and also the method of using the box sextant are described. The use of an echo-sounder to locate weed beds is discussed and the different types of record obtained over various types of bottom or weed are noted. The use of a viewbox and personal observation is also mentioned, and finally an account is given of aerial photography as a means of survey. The most suitable conditions for success are noted and also the technique of interpretation for both oblique and vertical photographs. The plotting of these two types of photograph is described in some detail.

The breathing, feeding, swimming, burrowing and cleaning habits of Cumopsis goodsiri are discussed.

Cumopsis has compact respiratory chambers. The inspiratory current enters each gill chamber posteriorly at the base of the third maxillipede, and the expiratory current leaves anteriorly through the siphons which pass through the pseudorostral chamber. The inspiratory current is filtered from all suspended particles by a sieve placed at the mouth of the respiratory funnel, which is formed by the depression of the third maxillipede away from the body. The size of the spaces in the mesh of this sieve probably determines the grade of the substratum in which the animal can live.

Cumopsis feeds on micro-organisms which it cleans off sand grains and other small objects. These are collected by the first peraeopods, held in position by the third maxillipedes, and cleaned by the first and second maxillipedes. The food is then passed on to the maxillae, maxillules and mandibles and finally enters the mouth. All these appendages are suitably armed to perform their respective functions.

Use is made of the last four pairs of peraeopods in burrowing and Cumopsis will only burrow into a sandy substratum. Swimming is accomplished in three different ways: (a) by flexures of the abdomen, (b) by paddle-like movements of the exopodite of the first peraeopod, and (c) in adult males by the abdominal pleopods.

The body is cleaned by the uropods. Their general rough surface and flexibility is very important. The uropod armature seems to add efficiency to the cleaning movements in the adult animals, particularly in the males.

The size of the soil particle is vitally important in the distribution of the Cumacea. It determines whether the animals breathe properly. There is also probably a close association between the soil grade and distribution of soil micro-organisms upon which they feed. As a result they refuse to burrow into a soil grade which is unfavourable.

A fungus has been found causing a fatal disease among mackerel in British waters, and a very high rate of infection has been maintained for over three years. It is spread throughout the viscera by the circulation, being particularly common in the kidney and spleen: it is very rare in the muscles and has never been found in the gonads or central nervous system of these fish.

Growth of the aseptate, sparsely branched hyphae is usually radial, from one of three types of central body. The length and thickness of the hyphae varies according to the density of the infected tissue and the degree of resistance which is set up. Connective tissue capsules are laid down round spores and hyphal bodies, occluding the small vessels or capillaries in which they become lodged. Growth of the parasite stretches the capsule, which may become a tubular gallery containing many growth stages. This may effectively seal the parasites which then degenerate; or, more usually, the strong proteolytic enzymes secreted by the advancing hyphae perforate it, and proceed to convert the whole organ into a necrotic mass in which hyphae grow to great lengths. There is always a tendency for hyphal walls to collapse behind the outgrowing hyphae, giving the appearance of hair-like threads with swollen ends.

Any of the following developments may occur, apparently on any hypha, in tissue undergoing necrosis: (1) Bunches of large elongated chlamydospores, with a very hard exospore and a thick (?) gelatinous endospore—a germination pore is present; (2) Single dome-shaped conidia (like those of Entomophthoraceae); (3) Hyphal bodies of various shapes, either growing at once where they become lodged or becoming rounded and encysted—these may subdivide irregularly, each spherule having a separate cyst; (4) Branched conidiophores with rounded tips which contain endo-conidia—liberated as minute amoeboid bodies into the blood vessels; (5) Simple clavate sporangia from the ends of unbranched hyphae, also containing endo-conidia; (6) Hyphal fusions of numerous kinds, immediately proceeding to further outgrowths of similar hyphae; (7) ‘Spores produced by hyphal fusion’: fusion of two hyphae followed by the participation of neighbouring hyphae which also contribute to form the outer, resistant, rugose wall.