300 



ANNELIDA. 



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

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

 the Clicetopoda. 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-oesophageal ganglion 

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

 the cesof hageal commissures are extraordinarily long. 



The strongly developed prseoral lobe forms a proboscisrlike 



FIG. 314. a, female of Bonfllia riridu (after Lacnzc-Duthiers). I, Integument and generative 

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

 Ad, rectum ; OP, ovary ; Tr, ciliated funnel of the uterus (17). c, Anatomy of iV/< /'/ n 

 tiridis (after Lacaze-Duthiers). D, alimentary canal with anal vesicles (Al) ; M, mesen- 

 tery ; U, uterus ; R, proboscis. 



appendage which may develop to a considerable length and become 

 forked (Bonellia} (fig. 314 a). 



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

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

 Echiurus there are also one or two circles of set3 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 



