A population of the lamellibranch Tellina tenuis in the Exe estuary is shown to be uniformly distributed, indicating a significant degree of ‘over-dispersion’.

By plotting the position of each shell in squares of m.2 area it is shown that fewer individuals than would be expected occur less than 1 in. from their nearest neighbour, and none occurs closer than 0·6 in.

When the population density was artificially increased on the shore the same characteristic spacing was found at a moderate density, but not at a rather higher density.

It is suggested that spacing is correlated with the foraging activities of the inhalent siphon on the soil surface.

Very dense populations have been found by Stephen in other areas, indicating that the size of the ‘territory’ does not limit density. His results show no evidence of the same phenomena as observed in the Exe.

A gregarious tendency during settlement, similar to that already demonstrated in oyster larvae, was suspected in Elminius, because cyprids settled in groups during the initial stages of colonization of surfaces (crowded later arrivals showed a spacing-out tendency) and because settlement on test-plates was peculiarly sparse at stations with a muddy bottom, where barnacles were absent.

Settlement was much heavier on areas of smooth glass, which already bore recently settled barnacles, than on similar adjoining areas which were bare.

When barnacled microscope slides were stuck to one set of glass plates, bare slides to another and the two sets exposed side by side, settlement was consistently much heavier on the plates which bore the barnacled slides. The mean density of settlement on the bare slides and the surrounding plates was uniformly low, except for a greater density immediately adjoining the slides, probably due to sheltering alongside their edges. On the barnacled slides density of settlement was much higher and on the plates immediately alongside still more so, whilst at increasing distances from the slides it became gradually smaller but was still much heavier than on the plates with the bare slides. This suggests that the sensory basis for gregariousness can act at a distance. It may possibly be olfactory.

A description is given of a glass cloth surface which prevents the settlement of larvae of Balanus crenatus and Pomatoceros triqueter, whilst not affecting that of Tubularia larynx. A number of possible causes for this are examined, and its relation to other work on the settlement of sedentary forms is briefly considered.

In Branchiomma vesiculosum decrease in light intensity causes the animal to contract and withdraw into its tube. A decrease, never an increase, in illumination is the effective stimulus. When repeatedly stimulated the animals quickly become adapted to intensity changes and no longer respond.

The minimal effective intensity change has been determined for a range of intensities. ΔI/I is found to increase in low light intensities, and to be fairly constant in intensities over 50 lux. The animals are least sensitive to red light; sensitivity increases in shorter wave-lengths.

An account is given of the reproduction and development of the larva of N. diversicolor O. F. Miiller.

In any one population the number of males was found not to exceed 10 %.

The species is dioecious. Both sexes become green at maturity, but may be distinguished externally.

Ripe oocytes, which vary between 200 and 250μ in diameter mature in a loose coelomic parenchyma, and are released by rupture of the body wall after its partial histolysis. Sperm is released through the nephridia, or possibly by rupture of the body wall as well. In the male histolysis occurs, but the coelomic parenchyma is transitory. Sperm matures in the form of coelomic sperm plates.

In Britain Octopus vulgaris occurs on the Channel coast and only very rarely on other coasts. In Brittany and the Channel Islands it frequently makes its lair at low water, but on the English side of the Channel it does not come so close inshore except in abnormal years of high sea temperatures.

The discovery of Octopus larvae of various sizes, from newly hatched to 6·0 mm. (mantle length), in plankton hauls taken to the north of the Channel Islands, proves that the species has a much longer planktonic life than hitherto supposed.

The water circulation in the English Channel, as indicated by drift bottles, is admirably suited to the dispersal of larvae to our shores from breeding centres on the coasts of Brittany and the Channel Islands.

Monthly samples of the common British Laminariaceae and Fucaceae taken during 1946 have been analysed for cellulose.

The cellulose content has been found to increase with the depth of immersion of the weed.

In the Laminariaceae, both in the stipe and frond it undergoes marked seasonal variation, exhibiting two maxima, March/April and September/October with a distinct minimum in June/July.

In Laminaria cloustoni, in March, maxima of 5·7 (dry basis) occur in the fronds and 10·3% in the stipes with minima, in June, of 4·1 and 8·4% respectively. In Laminaria saccharina the cellulose content (dry basis) varies between 4–5% in the frond and 7–8% in the stipe and in Laminaria digitata between 3–5% in the frond and 6–8% in the stipe.

In the summer of 1949 a compound ascidian was collected from the shore of Seil Island, Argyll. This proved to be a new species of the family Didemnidae. It is proposed to name it Lissoclinum argyllense, the specific name indicating the area in which it was first found. No species of Lissoclinum has hitherto been included in the British fauna.

The life histories of the small planktonic copepods of Plymouth were studied during 1947. The samples were taken at Station L4 with Harvey measuring nets, and are thus truly quantitative.

The main species concerned were Pseudocalanus elongatus, Paracalanus parvus, Centropages typtcus, Temora longicornis, Acartia clausi, Oithona similis, O. nana, Oncaea venusta and Corycaeus anglicus.

The species common in summer—all but the last three of the above—behaved in a very similar way, producing probably five generations in the course of the year, but differing from each other in the relative and absolute abundance of the different stages at different times of the year.

A certain variation in level of the fucoid zone with latitude is demonstrated. The belt of Fucus vesiculosus and F. serratus lies lower on the Devon coast than on either the Manx or the Argyll coast.

The conditions for the optimum germination of fertilized eggs are dissimilar to those for maximum rate of frond-extension.

Normal growth-rates have been established for both species for the first 3 years of life. In F. vesiculosus the average rate of elongation per week is 0·48 cm. on the Devon coast, 0·45 cm. on the Manx coast and 0·68 cm. on the Argyll coast. In F. serratus the average rate of elongation per week is 0·49 cm. on the Devon coast, 0·68 cm. on the Manx coast and 0·85 cm. on the Argyll coast. The rate of growth is shown to vary with the conditions of the environment. Shelter from rough water tends to enhance growth-rate, and there is an indication that greater stature is achieved by the plants from the Argyll station than from either of the other stations.