348 



SCIENCE 



[N. S. Vol. XXIX. No. 739 



which the young is not only a true larva, but 

 pelagic. The lobster also makes good use, but 

 in a different way, of a " lost larval molt," 

 which is shed at the time of hatching. In 

 this case also the molt sticks to the mother, that 

 is, to the inside of the inner egg-membrane or 

 chorion, and by being slightly adherent to the 

 setae or swimming hairs of the larva, helps to 

 pull them out or evaginate them, and thus 

 bring them into position for immediate use. 

 To escape merely from its egg-shells, without 

 losing in the proper manner this inner cuti- 

 cular molt, is as fatal to the lobster as the 

 premature breaking of the telson or anal 

 threads would be to the crayfish. 



The third stage in the crayfish corresponds 

 approximately to the fourth stage in the 

 lobster, in which the animal passes as if by 

 a sudden leap into the adult-like form, but 

 the transition is less abrupt in crayfishes 

 since their most striking larval characters 

 have been lost. 



In giving up the free-swimming habits of 

 their marine lobster-like ancestors, the cray- 

 fishes have apparently acquired their peculiar 

 family life, and a " crawling instinct " would 

 seem more in accord with the needs of many 

 of the species which inhabit fresh water- 

 courses liable to go dry, or which even burrow 

 deep in the ground to find the necessary 

 moisture. 



The larval history of Astacus is thought to 

 be "more primitive in having a more com- 

 plete representation of a lost larval stage still 

 evident in a complete cast cuticle within the 

 egg." But this cuticle is apparently not 

 homologous with that cast by the lobster at 

 birth, the pre-pelagic stage of this form being 

 represented by an egg-stage in Astacus. 

 Again, since the family life is more com- 

 pletely developed in Camharus, and the genus 

 is more specialized than in AstaciiS, " we may 

 therefore suppose," says Andrews, "that as 

 Camharus has migrated over the middle and 

 eastern United States it has become split up 

 into the sixty odd species now found and in 

 some, as in Camharus affinis, has made more 

 perfect the association of young and parent 

 already present in the Astacus ancestor." 



It is further suggested that the apparent 

 relation between acquisition of family life 

 and migration from the sea to fresh water 

 may be illusory, since metamorphosis has al- 

 ready been reduced in the marine lobsters, 

 and since in bays and estuaries which must 

 have been first encountered this dependent re- 

 lation would seem to be especially valuable. 



While it is easy to speculate on the origin 

 of the specific characters of crayfishes, and we 

 might add of any animals whatsoever, he con- 

 cludes that " the nature and the amount of 

 differences of the hard parts and in the larval 

 history that distinguish one kind of crayfish 

 from another are such as to raise the ques- 

 tion whether utility and natural selection 

 have played any part in their formation or 

 in their perfection. All the specific and 

 generic characters of crayfish may be as use- 

 less as color differences, and they may have 

 arisen suddenly perfected as we see them, or 

 they may have progressed in certain lines for 

 long periods of time independent of external 

 agencies." Much more evidence is needed be- 

 fore we can conclude that the various parts 

 and functions displayed "have ever in any 

 manner been connected with utility to the 

 species or with the survival or extinction of 

 individuals. Until the contrary is proven we 

 may therefore regard them as the unmeaning 

 by-products of unknown activities in the liv- 

 ing protoplasm." 



Such criticisms as are suggested in the 

 reading of this careful paper are of a minor 

 character. It does not seem proper to de- 

 scribe the invaginate matrix cells of the epi- 

 dermis which secrete the cuticular sheaths 

 of spines or set9e as " glands," since all the 

 superficial cells of the epidermis are chitin- 

 ogenous. Further, it would appear to be less 

 confusing to limit the use of the troublesome 

 term " larva " to the first two stages of the 

 young, and to designate as " adolescent " or 

 " adult-like " those stages in which the adult 

 characters appear most pronounced, unless 

 we resort to some such cumbersome termin- 

 ology as that proposed by Hyatt.^ It is cer- 

 tainly objectionable to designate as " larvse " 



' Science, N. S., Vol. V., p. 167. 



