CONTRIBUTION TO AN EVALUATION OF THE SEA. 323 



THE RATE OF GROWTH OF OYSTER SPAT IN THE 

 FIRST SUMMER. 



Besides the two experiments described above two other independent 

 ones were carried out, but without success, for the purpose of catching 

 Crepidula spat. These experiments, however, were successful in catching 

 a large amount of oyster spat and other marine invertebrates, and in one 

 case a few spat of the common cockle, Carditmi edule, which are of much 

 interest, were obtained. Measurements of the oyster spat have been 

 made and a growth curve will be given to show the variation in size in 

 spat of all ages up to 10 and 15 weeks. The limits of size of the 10-weeks' 

 spat — as determined by the area of one valve — are from about 2 sq. mms. 

 to 175 sq. mms., and the commonest size appears to be about 75 sq. mms. 

 The largest specimens of 15- week spat have an area of about 250 sq. mms., 

 i.e. about a square inch. Samples of these oysters are still being kept 

 under observation with the object of observing their subsequent rate of 

 growth and the age at which they begin to spawn. 



The spat of the C. edule mentioned above varied in their greatest 

 breadth between 24 mms. and 84 mms. and their greatest age is 15 

 weeks. Other observations on this mollusc, however, are being carried 

 out with the object of following more fully the rate of growth, and par- 

 ticulars will be given later. 



A large collection of various molluscs has also been made with a view 

 to investigating their age from the periodicity of the main lines of growth. 

 Some success has already been obtained with Patella vulgata, C. 

 Jornicata, C. edule, and the fresh-water mussel, Anodonta cygnea, in all 

 of which the periodicity of growth is well marked. In all these cases, 

 however, it is important to establish the rate of growth during the first 

 season, and, as has already been noted above, valuable information in 

 this respect has been obtained for Crepidula, Patella, Mytilus, Cardium, 

 and Ostrea. 



THE LIFE-HISTORY OF GALVINA PICTA. 



Some remarkable facts relating to the life-history of the Nudibranch 

 Molluscs have been obtained, and the following case may be taken as an 

 example. The raft moored in Cawsand Bay — mentioned above — was 

 visited six weeks after it was put out in the sea. It was found to be 

 covered with a large scattered growth of the hydroid Obelia geniculata, on 

 which the adult Nudibranchs, Galvina picta, G. exigua, Tergipes despectus, 

 G.farrani, and young Facelina drummondi and Doto coronata were feeding. 



NEW SERIES.— VOL. X. NO. 2. JUNE, 1914. X 



