The structure of the retina and tapetum lucidum of the teleost Howella is described. The tapetum is a diffuse reflector composed of lipid spheres. The photoreceptor layer of the retina contains only rods; in section the rods appear segmented, perhaps arranged in stacks but their precise arrangement remains to be determined.

On hatching, larvae of herring, Clupea harengus L., showed increased activity to washings and extracts of the nauplii of Balanus balanoides and to glycine and proline whichare major constituents of the free amino acid pool of Balanus. Older larvae, which were fed on the nauplii of Anemia salina, showed a response to extracts, but not to washings, of this prey; they also responded to six amino acids. The active constituents of prey extracts were found to be dialysable. Surgical section showed the olfactory system was responsible for behavioural responses in herring larvae of 21 mm (total length) to extracts of Anemiasalina. At all stages of larval life, herring showed increased activity to washings of other herring larvae. Juvenile herring showed a preference for a part of a tank containing water in which other juvenile herring had been held.

The marine rotifer Brachionus plicatilis Müller was grown bacteria-free in a chemostat with the alga Brachiomonas submarina, labelled with Co vitamin B 12, as the limiting nutrient.

Balaniger balticus gen. et sp.nov. (Prymnesiophyceae) is described on the basis of electron microscopy of shadow-cast whole mounts, prepared from water samples collected in October 1975 at localities in the western Baltic. The saddle-shaped cell has two smooth flagella and a short haptonema. The cell surface is covered with oval organic scales supporting calcified pyramid-like structures. Confirmation of the calcification of the periplast has been achieved by applying an X-ray analytical electron probe to one of the specimens observed.

Recent experimental measurements have confirmed the accuracy of earlier calculations of the extent of hydrolysis of ammonium ions in sea water over a range of temperature and salinity. Tables of the percentage of un-ionized ammonia in sea water compiled from the calculated data can therefore be used with confidence in assessing ammonia toxicity in mariculture systems.

Certain endomyarian sea anemones possess marginal spherules or acrorhagi (Stephenson, 1928) which are employed only in aggressive behaviour towards other Anthozoa. The acrorhagi can be dilated and movements of the oral disc and column bring them into contact with an adversary. Pieces of acrorhagial ectoderm adhere to the body of the adversary whilst discharging into it the large atrich nematocysts characteristic of acrorhagi. Such behaviour has been described in the European anemone Actinia equina (L.) and the Californian anemones Anthopleura elegantissima (Brandt) and Anthopleura artemisia (Dana) (Äbel, 1954; Bonnin, 1964; Francis, 1973). Aggression usually occurs only following repeated contact with a genotypically distinct anemone: mere proximity does not usually initiate any response (Francis, 1973).

I have recently seen similar behaviour, apparently not recorded before, in the European anemone Anthopleura ballii (Cocks) collected from Weymouth, England. Specimens were kept in an aerated aquarium with other anemones and fed irregularly: the behaviour observed occurred between 19.00 and 22.00 h G.M.T. during August and November 1977. Following contact between two specimens of different colour varieties and the subsequent use of acrorhagi by one of them, the light-coloured passive individual immediately moved away from the dark-coloured aggressor and remained partly contracted with a ‘withered’ appearance to the tentacles for 1 week, following which it recovered (August). The same aggressor later (November) attacked a Cereus pedunculatus (Pennant), causing it to detach immediately from the substrate and to become necrotic one day later. The Cereus remained detached with the tentacles retracted and the column swollen for 5 days before it recovered.