490 



ZOOLOGY 



system comprises a large stellate ganglion 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 



Fro. ::-i. Myzostoma. I-X, i-in-i ; m. month ; p. parapodift ; ». suckers. (After von Graff.) 



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 a pair of 

 ovaries formed by the proliferation of the layer of (coelomic) 

 epithelium covering the stomach ; and in the sexually mature 

 animal branching (coelomic) spaces in the parenchyma, between 

 the caeca, are found to be filled with ova (o). A posterior continua- 

 tion of these spaces (u) opens either into the cloaca or independently 

 of it. There are two elongated and usually branched testes (A), 

 each of which has two vasa deferentia leading to a vesicula 

 seminalis (sb) which opens near the lateral margins. The sexes 



