Chapter XII.— THE HISTORY OF THE LARVAE AND EARLY ADOLESCENT 
PERIODS. 
The transition from the caterpillar to the chrysalis and from this to the winged 
butterfly or moth is apparently so sudden 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 castoff; 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, aud 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. 1 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 J or § 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, Astac us 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, Pahemo n, 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 a frontal spine, spatulate 
tail, and wanting subabdominal fins; 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 (21) 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 Rathke 
in 1840 (159), and a fuller account with figures of the embryo and of some of its append- 
ages appeared in 1842 (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 
aud 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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