390 



ANNELIDA. 



fact, as well as the formation of the prseoral lobe and the develop- 

 ment of the ventral hooked seta?, points to a close relationship with 

 the Clifvtopoda. In the adult animal, however, the internal segmen- 

 tation is very little marked. The dissepiments, with the exception 

 of the first, which forms a partition between the head and the body, 

 are lost, and the segmentation of the ventral cord is only indicated 

 by the distribution of the nerves. The supra-cesophageal ganglion 

 remains at the apical region of the pneoral lobe (proboscis) ; hence 

 the oesophageal commissures are extraordinarily long. 



The strongly developed piworal lobe forms a proboscis -like 



FIG. 314. a, female of BoneUhi viriHis (after Lacaze-Duthiers). I, Integument and generative 

 organs after the intestine has been removed. Hd, Cutaneous glands ; Al, anal vesicle'; 

 Ad, rectum ; On, ovary ; TV, ciliated funnel of the titerus (V). c, Anatomy of BoiifUin 

 viridi* (after Lacaze-Duthiers). D, alimentary canal with anal vesicles (Ab) ; M, mesen- 

 tery; U, uterjs; .R, proboscis. 



appendage which may develop to a considerable length and become 

 forked (Bonellia) (fig. 314 a). 



A pair of hooked set* (with reserve seta? in the sheath of each 

 seta) are always present on the first segment of the body. In 

 Ecliiurus there are also one or two circles of set* at the posterior 

 end of the body. There are from one to three pairs of anterior 

 segmental organs (so-called brown tubes or ventral glands), which 

 open on the ventral surface and are used for the passage outwards 

 of the generative products. Besides these there is also a pair of 



