REPRODUCTION AND GROWTH 277 



eggs, while a large American Oyster has been computed 

 to contain more than 100,000,000 ova (Woodward, 1913). 

 There is, however, a point in connection with the growth 

 of forms such as the oyster, mussel, and cockle which deserves 

 notice. As the animal increases in size, the shell, of course, 

 is enlarged pari passu by the addition of successive areas of 

 lime secreted by the edge of the mantle. From an examina- 

 tion of these " growth " lines and from the general appear- 

 ance of the shell a considerable amount of information can 

 be gained as to the age of the molluscs and the suitability 

 or not of the conditions in which the animal has been 

 growing. Mussels which, owing to unsuitable conditions 

 of temperature, food, or salinity, remain small and stunted 

 in size will, when transplanted to suitable areas, grow to 

 marketable size in a very short time. 



Fishes. — Shore fishes are not particularly fecund but 

 the comparatively small number of ova produced is perhaps 

 compensated by the care which is bestowed on them by 

 the parents. Notwithstanding parental care, however, the 

 mortality among eggs and young is very great. M'Intosh 

 (1901), in fact, considers that no group of marine fishes is 

 better fitted for demonstrating the great losses which ensue 

 between the period of the deposition of the ova and the adult 

 condition than the littoral fishes, such as the Shanny, Cottus, 

 Gunnel, and even Viviparous Blenny. To take the Shanny, 

 for instance : notwithstanding the fact that the adult females 

 deposit a considerable number of eggs in small rocky caverns, 

 and that the young while still more or less pelagic abound 

 in the rock pools in August and September, yet frequently 

 only a single adult is encountered in a shore pool. This 

 decrease in numbers M'Intosh attributes not so much to 

 the fish becoming spread out in the ocean or to their taking 

 advantage of new sites among the rocks, as to the onslaught of 

 predatory neighbours. 



A similar disproportion is observable between the 

 numbers of young (eggs or larvae) and of adults of most shore 

 fishes. The demersal eggs of the short spined Cottus 

 {Cottus scorpius) are said by M'Intosh {loc, cit.) to be a 



