192 ANIMALS WITH JOINTED LEGS— THE ARTHROPODS 



Reproductive System. The male reproductive organs consist of a 

 pair of testes lying just under the heart and a vas deferens leading from 

 each to an opening in the base of the fourth walking leg. The sperms are 

 removed from this opening and transferred to the female by the first two 

 pairs of swimmerets which are modified in the male for this purpose. 

 The female system consists of the paired ovaries and an oviduct lead- 

 ing from each to an opening in the base of the third walking leg. Also, 

 there is a seminal receptacle on the ventral surface of the body between 

 the bases of the fourth and fifth walking legs. 



During the breeding season, which is usually in the fall, the male 

 will approach the female and a struggle follows with the female appar- 

 ently making a great effort to resist his advances. However, her re- 

 sistance finallv weakens and the male throws her over on her back. As 



Photo by Winchester 



Fig. 13.8. Regeneration in the crayfish. The right cheliped, which has been torn off, 



is in the process of regeneration. 



he stands over her, sperms flow from the openings of the vasa deferentia 

 and are guided into the seminal receptacle of the female by the first two 

 pair of swimmerets which are modified for this specific function. The 

 sperms are kept here through the winter months and fertilize the eggs in 

 the spring. When the proper time arrives for egg-laying, the female 

 first secretes an adhesive substance from the basal portion of the uropod. 

 This is spread over the swimmerets. Then the crayfish turns on her 

 back and lays the eggs which are passed backward over the seminal re- 

 ceptacle to receive the sperms which were deposited there. They are 

 then guided back and stuck onto the swimmerets by the adhesive which 

 covers them. During the embryonic development of the young crayfish 

 within the eggs, the female waves the swimmerets back and forth in the 

 water in order to keep the embryos well supplied with oxygen. Upon 

 hatching, several months later, the young crayfish cling to the swim- 

 merets of the mother until after their second molt. 



