PHYLUM ANNULATA 



44!) 



situated ventrally, probably representing a number of fused ganglia, 

 and giving off a number of nerves ; and of two nerve-rings, one 

 round the oesophagus, the other round the pharynx, the two rings 

 being connected together by a series of longitudinal nerves : the 

 oesophageal ring presents a very obscure dorsal thickening, which 

 is the only representative of a cerebral ganglion. 



Most of the Myzostomida are hermaphrodite. There is some 

 doubt about the position of the ovary, but in the sexually mature 



FIG. 350. Myzostoma. (After von Graff.) 



animal branching spaces in the parenchyma between the caeca are 

 found to be filled with ova (o). A large uterus (u) opens into the 

 cloaca by three ducts. There are two elongated and usually 

 branched testes (h), each of which has two vasa deferentia leading 

 to a vesicula seminalis (sb) which opens near the lateral margins. 

 A few species are dioecious. In one species, in addition to the 

 ordinary hermaphrodite individuals, there are much smaller males 

 the " complemental males." 

 VOL. i G G 



