CONTRIBUTION TO AN EVALUATION OF THE SEA. 319 



age yielded 100 per cent of fertilized eggs. At this age the commonest 

 sizes are from 3-5 to rather more than 4 cms. A good deal of material of 

 this species has been obtained continuously during a period of two years, 

 so that it will be possible to work out the rate of growth in this important 

 mollusc fairly thoroughly. From several independent experiments it has 

 been found that M. edulis may grow in this district to a size of from 3-5 

 to 4 cms. within the period between April and November, i.e. in about 



30 weeks. During the winter it would appear that relatively little 

 growth takes place. By the following April, however, specimens may 

 attain to the size of upwards to 5 cms., and at the end of the summer 

 following that in which the animals were spawned, i.e. at an age of about 

 18 months, the average length of specimens is about 5 cms. with a 

 corresponding increase in width and depth, while one specimen of this 

 age attained a length of 6-8 cms. and a width of 3-4 cms. The variations 

 in size at different ages will be given later. An interesting comparison 

 has been made between mussels 3-5 cms. long and about 10 months old 

 and thick-shelled mussels from 1-3 to 1-6 cms. long from the exposed 

 shore at Wliitsand Bay. The latter were quite ripe and gave good 

 fertilizations, whereas at the same time the former were not ripe. Thus 

 it would seem that the Whitsand Bay specimens really were dwarfed 

 individuals of an age of at least two years. 



Continuous observations have also been made on the rate of growth 

 in a few individuals of the common limpet. Patella vulgata. It has been 

 found that specimens may attain a size of 4 cms. in less than 15 months, 

 and at this age are ripe. An artificial fertilization made from these 

 specimens gave ultimately a fair percentage of trochospheres. During 



31 weeks between the 27th January and the 2nd September, 1913, two 

 specimens grew on a fiat surface, respectively, from (a) 2-1 cms. long by 

 1-6 cms. wide to 4-1 cms. long by 3-3 cms. wide, and (h) 3-8 cms. long by 

 3-2 cms. wide to 5-3 cms. long to 4-5 cms. wide. Thus the smaller 

 specimen increased 2 cms. in length and the other 1-5 cms. in length. 

 The age of the latter specimen when 5-3 cms. long was not more than 

 two years. Another specimen grew between April 4th and September 

 2nd in the same year from 2-25 cms. long by 1-7 cms. wide to 3-3 cms. 

 long by 2-85 cms. wide, thus increasing in length 1 cm. within 20 weeks. 

 Thus the rate of growth of P. vulgata in this district is much greater — 

 as indeed might be expected — than that found by Russell* in Scotland. 

 These observations are, however, being continued, and the results in 



* E. S. Russell, "The Growth of the Shell of Patella vulgata" Proc. Zool. Soc, 1909, 

 p. 235, I. 



