TYPE ANNELIDA. 



245 



likewise surrounding the oesophagus and apparently represent- 

 ing the supracesophageal ganglion. Numerous longitudinal 

 nerves pass forward from the ring to unite with another ring 

 around the base of the proboscis from which nerves pass to 

 the tentacles. Below the intestine lies a large ganglionic mass 

 with which the circumo3sophageal commissures unite and 

 which gives off a number of peripheral nerves. This mass is 



mo 



ov 



fo- 



do 



FlG. 111. Myzostomum (after VON GRAFF). 



c = cirrus. v = rectum. 



do = cloacal opening. 

 fo = opening of uterus iuto cloaca. 



o = opening of male reproductive organs 



p = parapodium. 



pJi = proboscis. 



s = stomach. 

 su = sucker. 

 t = testes. 

 u = uterus. 



composed of several (probably 6) united ganglia and represents 

 the ventral nerve-cord of other Annelids. Nerves pass pre- 

 sumably from the supracesophageal ganglion-cells along the 

 dorsal wall of the intestine and seem to constitute a sympa- 

 thetic system. The only structures which can be considered 

 sense-organs are the marginal cirri and the tentacles of the 

 proboscis, which probably have a tactile function. No traces 

 of eyes have yet been observed. 



Nephridia, unless they be represented by the sucker-like 

 depressions aud the oviducts, are wanting. The Myzostomeje 



