Chapter XII.— THE HISTORY OF THE LARVAL AND EARLY ADOLESCENT 



PERIODS. 



The transition from the caterpillar to the chrysalis and from this to the winged 

 butterfly or moth is apparently so sadden that it strikes every one with wonder. This 

 is, however, deceptive, since changes in the internal organs go on very slowly. The 

 hard supporting skin of the chrysalis masks the changes which are taking place within. 

 The young crustacean, on the other hand, has a soft cuticle which is readily cast off; it 

 thus changes with every molt and in most cases acquires very slowly the external form 

 and habits of the adult state. It is therefore possible to follow its metamorphosis 

 step by step. For convenience I shall divide the life-history into three periods — the 

 larval, adolescent, and adult. The larval period will embrace the free-swimming life, 

 during which the animal molts five or six times, and the adolescent state the long 

 interval thereafter before sexual maturity is reached. 



The larval history of the lobster is one of exceptional interest and importance, 

 and must be thoroughly understood before the problem of hatching and rearing the 

 young can be intelligently discussed, much less solved. I therefore decided, at the 

 beginning of this work, to devote as much attention as possible to this part of the 

 subject. This seemed particularly desirable since the individual larval history had 

 never been traced molt for molt; only four pelagic stages had been described, and the 

 relations of these were not fully understood. Of the later adolescent period (length 

 of animal £ or f inch to 2£ inches) nothing, as we have just seen, was definitely known. 



HISTORICAL NOTES. 



J. V. Thompson, who was first to establish beyond any doubt the important fact 

 that the decapod Crustacea underwent a metamorphosis after hatching from the egg, 

 was also the first, so far as I am able to learn, to point out that the European lobster 

 was no exception to this very general rule. His letter (published in 1835) to the editor 

 of the Zoological Journal is dated at Cork, December 16, 1830. A "rough sketch of 

 the cheliferous member of the larva of the lobster" accompanies this letter. He says: 



With regard to the marine species, Astacus marinus or Lobster, I can aver that it actually does 

 undergo a metamorphosis, but less in degree than any of the above-mentioned genera (Pagurus, Por- 

 cellana, Galathea, Crangon, Palremon, etc.), consisting in a change from a cheliferous Schizopode 

 to a Decapode; in its first stage being what I would call a modified Zoe with afrontal spine, spatulate 

 tail, and wanting subabdomiual tins; in short, such an animal as would never be considered what it 

 really is were it not obtained by hatching the spawn of the Lobster. (189.) 



Brightwell (24) gave in 1835 a very imperfect description of the young lobster 

 which he dissected from the egg membranes. He was the first to notice the occur- 

 rence of double monsters in this species. (See p. 216.) 



The embryo of the European lobster when ready to hatch was described by Eathke 

 in 1840 (159), and a fuller account with figures of the embryo and of some of its append- 

 ages appeared in 1812 (160). He found lobsters with external eggs in early stages of 

 development at different times of the year — at the end of May in Christiania, in June 

 and July at Molde and Christiansund, in September at Gothenburg, and in the first 

 half of October in Hamburg. He therefore concluded that lobsters either laid their 

 eggs at different times of the year or that their development was very slow. 



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