The Crayfish. 49 



duct, which carries the generative products to the exterior. 

 These ducts are long and much coiled in the male ; short in 

 the female. It is believed that the cavity of the generative 

 gland is ccelomic in nature. This conclusion has been arrived 

 at from a consideration of the formation of the gonad in 

 animals. The gonads are, as already pointed out to be, 

 regarded as local proliferations of the ccelomic epithelium, 

 either restricted to a limited area, as in the earthworm, the 

 vertebrate, etc., or spreading through the whole, or nearly the 

 whole, of the body, as in certain marine worms. If this portion 

 where the generative tissue is formed be separated from the 

 rest of the body, and the coelom obliterated elsewhere than 

 here, we arrive at a structure like that of the crayfish, where, 

 moreover, it will necessarily follow that the oviducts, or sperm 

 ducts, opening into this intra-gonadial region of the coelom will 

 get the appearance of being merely prolongations of the gonads 

 themselves (see also p. 159)-. 



