334 



PHYLUM ARTHROPODA 



mother keeps her tail bent till the eggs are glued to the 

 small swimmerets. 



Before this, however, sexual union has occurred. The 

 male seizes the female with his great claws, throws her on 

 her back, and deposits the seminal fluid on the ventral 

 surface of the abdomen. The fluid flows down the canal 

 formed by his first abdominal appendages, and these seem 



Fig. 1 78. — Section through the egg of Astacus after the com- 

 pletion of segmentation. — After Reichenbach. 



si., Stalk of the egg ; ch., chorion envelope ; bl., peripheral blastoderm 

 within which are the yolk pyramids (dark). 



to be kept clear by the movements of the next pair, which 

 are also modified. On the abdomen of the female the 

 agglutinated spermatozoa doubtless remain until the eggs 

 are laid, when fertilisation in the strict sense is achieved. 



The Development has been very fully worked out, and is of interest 

 in being direct, without the metamorphosis so common among the 

 Arthropoda. The spherical ovum is surrounded by a cuticular vitelline 

 membrane, and contains a considerable quantity of yolk. After ferti- 



