THE CRAYFISH 



153 



Exercise 8. — Embryonic and Juvenile Stages. 



(b) The spermatozoa are transferred from the male to the female 

 during sexual union and retained in the seminal receptacle where they 

 are available at the time of egg-laying. The ova are fertilized as laid, 



Fig. 68. — The development of the crayfish. A and B, ventral view of eggs, 

 showing early stages in the development of the appendages and the principal 

 divisions of the body. C, mass of young crayfish upon a swimmeret of the 

 mother. D, second larval stage (2) attached by its chelipeds to hairs (s) on 

 a swdmmeret (p) of the mother. The molted shell of the first larval stage 

 (1) is seen clinging by its chelipeds. The remains of the egg-membrane (m) 

 and egp-.shell (sli) are still attached to the hairs of the swimmeret by a stalk 

 (st). When the first larva hatches it remains attached to the shell by a 

 filament {t. /.) until its chelipeds can grasp a hair, and the second larva is 

 similarly attached to the molted shell of the first by a filament (a. /.) By 

 means of these filaments the young remain fastened to the mother during 

 the periods of development when they might easily become detached. E, first 

 larva hatching through a break in the eggshell (sh), which is attached to a 

 swimmeret of the mother by a stalk (si). F, second larval stage. 



(A and B, redrawn from G. B. Howes, "Atlas of Zootomy," copyright, 1902, .by Mac- 

 millan and Co., Ltd., printed by permission; C to F, after E. A. Andrews, 1916, Smithsonian 

 Contributions, vol. 35.) 



