336 



ZOOLOGY 



SECT. 



internally in a flame-cell. The nervous system consists of a large dorsally and 

 anteriorly situated cerebral ganglion or brain giving off a pair of ventro-lateral 

 longitudinal nerves. The sexes are united, and there is no metamorphosis. 



Fia. 272.— Chaetonotus maximus. 



Highly magnified. (After Zelinka.) 



Fig. 273.— Chaetonotus maximus (or- 

 ganisation), brn. brain ; gld. adhesive 

 gland ; mes. mesenteron ; mo. mouth ; 

 ces. oesophagus ; ov. ovum ; ovar. ovary ; 

 retr. retractor muscles ; vent. mus. ventral 

 muscle. (After Zelinka.) 



APPENDIX TO THE TROCHELMLNTHES. 



The Dinophilea and Histriobdellea. 



These are two isolated groups of minute animals which may most conveniently 

 be dealt with in association with the Trochelminthes, since they bear certain 

 striking resemblances, now to one, now to another, member of that phylum ; 

 but they differ from all of them in the assumption of a simple kind of meta- 

 merism (p. 43), by virtue of which they have claims to association with the 



