OTHER CRUSTACEA 



333 



L 3 



i 3 



U D 



B 



"-— ' A ? 



D 



Fig. 161. — Development of crayfish. 



A and B, early embryonic stages showing origin of appendages and principal divisions 

 of body as seen from ventral view on surface of the spherical egg. C, mass of young cray- 

 fish upon a swimmeret of the mother (<-/. Fig. 15.5). D, second larval stage (2) attached by 

 chelae to hairs on swimmeret of mother. The molted shell of the first larval stage (1) is 

 seen chnging by its chelae. Notice, also, the remains of the egg shell and the stalk by which 

 the eggs are fastened to the hairs of the swimmerets at the time of laying. When the first 

 larval stage hatches it remains attached to this shell by a filament ((./.) until the chelae have 

 secured their hold. After the first molt, the second larval stage is in turn held securely by 

 another filament (a./.) until its chelae become attached. By means of these filaments the 

 young remain fastened to the mother during the brief periods of development when they 

 might easily become detached. E, first larval stage hatching through break in egg shell. 

 F, second larval stage. 



1, cast shell of first larva; 2, second larva; AB, abdomen; a./., filament of second larval 

 stage; AN and AN', antennse and antennules; LB, labrum or upper lip; m, membrane 

 inside shell; MD, mandible; OP, eye; p, swimmeret; AB, papilla-like beginning of 

 abdomen; s, hairs of swimmeret; sh, shell; st, stalk of egg; T.AP, thoracic appendage; 

 /./., broken filament of first larval stage; }', yolk. (A and B, redrawn from Howes, ".Atlas 

 of Zootomy," copyright, 1902, by Macmillan and Co , Ltd., printed by permission; C to 

 F, after Andrews, Smithsonian Contributions, Vol. 35, 1916. J 



