26 GENERAL REMARKS ON THE EGGS OF MARINE FISHES. 



triment, which must be a very costly necessity to the young 

 fish, as a source of attraction to many a hungry foe (see 

 Herring). 



The post-larval period extends from the end of the larval 

 period till the time when the adult characters are assumed. 

 This period is marked by numerous 'larval organs,' e.g. spines 

 and pigmentations, which disappear before the adolescent stage, 

 and must be regarded as secondary adaptations to the sur- 

 roundings of its youth, affording, in the wide sense, means 

 of defence or safety. 



At the adolescent stage the young fish has arrived at an 

 age when it is to all appearances an exact miniature of the 

 adult, and further changes take place mainly in growth and 

 maturation of the reproductive organs, though there may be 

 important changes in the relative size of various organs and 

 in pigmentation. 



In the progress of the evolution of a fish from the moment 

 of its individual existence to the adult stage we have care- 

 fully to distinguish the processes which take place side by 

 side but which are quite different in their nature, namely 

 development and growth. In the former we see the evolution 

 of new organs and the progress of each to greater complexity, 

 form and function rapidly differentiating till the adult stage 

 of organism is reached. In the latter we have cell-division, 

 resulting in increase of bulk, which continues long after the 

 development, in the strict sense, has come to an end, namely 

 at the end of the post-larval period, and which in fishes 

 there is reason to believe only terminates with the death of 

 the animal. In more highly organised animals, as birds and 

 mammals, there is a fixed limit of growth when we may say 

 that the organism has reached maturity and when the re- 

 productive organs come into functional activity, and beyond 

 which there is no further normal increase of bulk, but in the 

 case of fish the size attained seems to depend largely upon 

 the amount of nutriment consumed and upon the time over 

 which the active consumption extends. Thus the size of a 

 fish except in the widest limits is no criterion of the stage 

 of its sexual maturity nor even of its age. It is to be noted 



