Chap. XIII.] GONADS OF WORMS. 489 



male cells, while the rest forms merely an efferent 

 duct, or has its distal portion widened out into a 

 reservoir or seminal vesicle. The male orifice is, 

 however, associated with that of the intestine, and 

 two chitinous spicules are developed to serve as copu- 

 latory organs, and to aid in the entrance of the 

 spermatozoa, which here are always amoeboid in form, 

 and have no specialised mobile tail. 



The Acanthocephali are, again, examples of 

 forms in which the sexes are separate and the males 

 provided with a copulatory organ, but they exhibit so 

 much advance in structure as is implied by the testes 

 being two definite sacs; these, however, are not 

 paired, but one lies in front of the other ; the testes, 

 like the ova, are developed on a special cord 

 (ligamentum suspeiisoriuiii), the exact signifi- 

 cance of which is very incompletely understood ; a 

 somewhat similar structure has been observed in the 

 Bryozoa ; in the Chsetognatha we find that the testes 

 are developed in the anenterous or caudal segment 

 of the body, and the ova in the segment in front ; in 

 the Rotifer* the males are always without an 

 intestine. 



In the Nemertinea, the Oephyrea, and the 

 polychaetous Chsetopods the generative pro- 

 ducts are developed directly from the epithelial cells 

 lining the body cavity, and there is no definite region 

 of which one can speak as testicular or ovarian ; in 

 these cases, moreover, the sexes are, as a rule, sepa- 

 rate ; and we have herein some support for the view 

 that the hermaphroditism of many worms has been 

 secondarily acquired. 



In the Hirudinea and the oligoehsetous 

 Cheetopods we find, on the other hand, that the 

 generative products are developed in certain segments 

 only, and here, too, we find that the two sexes are 

 united in the same individual. Taking as types of these 



