Breeding in marine animals has long been recognised in a vague way as being in some degree dependent upon sea-temperature. This attitude is well shown in Lo Bianco's last valuable contribution to our knowledge of the breeding periods of practically the whole fauna of the Gulf of Naples. In the Introduction to this work Lo Bianco (1, p. 531) gives tables of temperature observations for a number of years, but does not attempt to correlate them with the breeding periods observed. There are in the literature some observations of reproduction in particular animals being dependent upon particular temperatures, notably by Schmidt (2); but no attempt has been made, so far as I know, to show in a general way the connexion between breeding and temperature in marine animals. It is clear, however, from the writings of Appellöf that this naturalist had anticipated in his mind some of the results obtained from the experimental observations described briefly in the following pages and of the deductions made therefrom. It is believed that these experimental observations have afforded a clue which gives an insight into the way in which breeding may be correlated with temperature in a large number of marine animals, but owing to the inadequacies of breeding records and of observations on physical conditions in the sea only a brief survey has been attempted here, and a fuller discussion of the phenomena is reserved for a later work. In the following pages the extrusion of ripe ova, or the fertilisability of eggs with subsequent development, is taken as the criterion of breeding.

Some preliminary observations in North Cornwall (Orton, 1946) showed that the periods of breeding of the three British species of limpets were different. In order to determine these differences more accurately, and to study the breeding cycle, samples oflimpets from six localities in Britain were examined at regular intervals for 5 years. This paper gives the results obtained for the common limpet Patella vulgata, which was present at all the localities sampled and was the most intensively studied of the three species. Later papers will deal with the remaining species and with other aspects of the investigations.The work fell rougWy into two stages. For.the first season, 1945-46, it was necessary to determine exactly the distribution of sexes in the various sizegroups at the different stations, since it was known that at Plymouth the small sizes were preponderantly male (Orton, 1920(Orton, , 1928 and rougWy equal numl?ers of both sexes are desirable for regular observations on breeding. At the same time the opportunity was taken to re-investigate sex-phenomena which had been noted previously and thought to indicate a change of sex during the life-history (Orton, 1920(Orton, , 1928. For the remaining period of study emphasis was placed on determining the exact period of spawning in the various localities, and on possible spawning stimuli.Although J. H. O. collected most of the samples that were taken personally, as distinct from those collected by other professional or amateur collectors, all three authors have taken part in the field work. J. H. O. was mainlyresponsible for the examination of the gonad stages, their grouping, and the calculation of the various numerical factors, J. M. D. carried out the histologicalwork and described the arbitrary stages, whilst A. J. S. analysed the breeding cycle and explored the relationship between meteorological factors and spawning. This paper has been prepared by A. J. S. and J. M. D., who are responsible for all opinions expressed herein.

On October 28th, 1920, a conjoint meeting was held by representatives of the Development Commission, the Ministry of Agriculture and Fisheries and the Oyster Merchants and Planters Association to institute investigations into the cause of the abnormal mortality which had occurred among oysters in the oyster beds in the Thames Estuary during the summer of 1920. As a result of this meeting investigations were begun under the general direction of the writer. On the completion of the work a full report of the results obtained was forwarded to the Fisheries Department, Ministry of Agriculture and Fisheries. The more important parts of that report will be published as follows: Part I, Main Report, Fishery Investigations, Ministry of Agriculture and Fisheries, London, Series II, Vol. VI, No. 3, 1923; Part II. containing the more important Appendices, will appear later.

An investigation of the rate of growth in Marine Invertebrates was begun in 1911, and a large amount of material the age of which is known has now been collected from various sources. The particular objects of this research are: (1) to establish the age of common marine invertebrates, (2) to determine the minimum age at which these forms begin to breed, (3) to examine the rate of growth at different seasons of the year and under different conditions, (4) to investigate the fecundity of different forms so far as possible, and (5) to collect the scattered literature on these subjects.