1. The seasonal changes in the population of Calanus in Loch Striven in 1933 have been investigated.2. There were three main breeding periods. The first was in February and March, an unsuccessful beginning of the second in April, the true second brood in May to June, the third in July, and subsidiary broods in August and September.3. Numbers were very low until April when the copepodites of the first brood caused a large increase; there was a second increase in May consisting mainly of the eggs of the second brood, and the maximum for the year came in July. The last and subsidiary broods provided the stock for the autumn and winter of 1933.

Attention was first drawn by Wilson (1932) to the large copepod fauna which can be found in an ordinary sandy beach. In his introduction he describes his method of collecting these copepods (p. 7) and in the course of the paper describes a number of new genera and species thus obtained.Sand-dwelling animals, particularly Crustacea and worms (excluding sessile forms), are usually regarded as burrowers, since in their migrations they displace the particles of their environment. The fauna opened up by Wilson's discovery is of a quite different type. In contrast to true sand-burrowing animals, these copepods do not displace the particles of the sand through which they move but crawl over the surface of the grains, which, by capillarity, always hold more or less water, even high up on the beach at low tide. Such copepods, together with nematodes, rotifers, protozoa and other animals sufficiently small, may be regarded as part of an “interstitial” fauna.

SUMMARY1. Experiments have been done to determine the oxygen utilisation by male, female and Stage V Calanus under different environmental conditions.2. An initial fall in the respiration of adult Calanus was observed during the first few hours after capture. Stage V do not show this clearly. It is found more often in winter than in summer.3. The lethal temperature varies from 24° C. in winter to 26° C. in summer. Stage V Calanus are more resistant to high temperatures than adults.4. Respiration rises with increase of temperature from 0° C. to 20° C. The increase does not follow van't Hoff's law. The oxygen consumption of males and females is about the same, while that of Stage V is lower. Above 20° C. there is a harmful effect.5. Within the limits studied (pH 7.4–pH 8.5) change in hydrogen-ion concentration has no effect on respiration.6. Calanus are unaffected by an increase in the oxygen content of the water, but are sensitive to low oxygen tensions. Below a concentration of about 3 ml. per litre the respiration decreases. At concentrations between 1 and 2 ml. per litre they are killed. They are more resistant at 5° C. than at 15° C. and Stage V are more resistant than adults at both these temperatures.7. Calanus can become acclimatised to salinities as low as 35–40% seawater (S=12‰–13.6‰), but their respiration is lowered at a salinity of 50%.8. Light has a striking effect on Calanus. It may increase the respiration by 100% or more. This effect can be detected also in the sea, but not below 5 metres. Continuous exposure to light is harmful.9. The bearing of these results on the distribution of Calanus is discussed.10. From the amount of oxygen used in respiration, calculations of the food required are made and these are compared with the results given by Putter for Calanus and other copepods.

1. Samples of herring from the Clyde sea-area were obtained weekly from the time of hatching in March until metamorphosis in June.2. The rate of growth was regular, about 3 mm. in length per week; the development was similar to that described from elsewhere.3. The herring which hatched off the south-west of Arran gradually moved northwards into the mouth of Loch Fyne and remained there until metamorphosis.4. The proportion feeding was usually small. The food consisted mainly of copepods, both young stages and adults. The size of the food organisms eaten depended roughly on the size of the herring

1. Previous work on vertical distribution and diurnal migration is described.2. The diurnal migration of Calanus was studied on two occasions in Loch Fyne (January and July, 1932).3. Vertical hauls were taken every three hours with a closing net dividing the total depth into six sections.4. The results for each copepodite stage of Calanus are discussed, and January and July conditions are compared where possible.5. Ova and nauplii were observed to be most abundant in the top 30 metres.6. Copepodite Stages I, II, and III were most abundant above 30 metres and only the third copepodites showed any tendency to descend as the light increased.7. Stage IV showed a migration towards the surface at night, but were generally distributed during the next day.8. It is suggested that the results for this stage are probably confused owing to its transitional nature between the young stages living at the surface and Stage V Calanus living in deep water.9. Stage V was found always in deep water, slight diurnal changes being ascribed to the presence of such Calanus as were about to moult into adults.10. Females showed definite diurnal migration in both January and July.11. Males showed a general distribution and migrated in small numbers towards the surface at night and away from it during daylight.12. Stage V copepodites and females both lived nearer the surface in January than in July, correlated with seasonal changes in the intensity of the sunlight.13. The presence of swarms of Calanus at the surface under conditions of bright sunlight is discussed.