DESCRIPTIONS OF GENERA AND SPECIES 297 



Definition Length 6mm. ; number of segments 38. First pair of ventral setae bundles larger 

 than those in two following segments ; those of IV very small, sometimes absent. Hab. 

 Europe, 

 This species has been chiefly investigated by VEJDOVSKY. 



Genus DERO, OKEN. 

 Syn. Proto, OERSTED. 

 TTronais, GERVAIS. 

 Xantho, DUTROCHET. 

 Aulophorus, SCHMARDA. 

 Nais, O. F. MULLER (in part.). 



DEFINITION. Dorsal setae capilliform and hastiform, commencing upon the sixth 

 segment. Branchial processes present at hinder end of body. Eyes absent. 

 Inhabit tubes 



The principal character of this genus is, of course, afforded by the branchial 

 processes at the end of the body, which are dorsal in position. These are ciliated 

 processes of the integument containing blood-vessels ; they really spring from the 

 expanded and funnel-shaped termination of the anus, and there are rarely more 

 than four of them (only in D. multibranchiata). Sometimes the occurrence of six 

 or even eight branchial processes has been asserted. In such cases it is the margin 

 of the funnel-shaped expansion, which is drawn out into processes ; a pair of these 

 are extraordinarily long in Dero furcata. The members of this genus usually (1 always) 

 inhabit tubes, which are formed by a viscid secretion from the worm's body to 

 which small extraneous particles adhere. A species investigated by myself (25), of 

 whose identity I am not certain, was invariably found in the interior of the stems 

 of dead and decayed aquatic plants. D. vaga walks about with its tube like a Caddis 

 worm. The genus is also to be characterized by the complete absence of floating peri- 

 visceral corpuscles (except in D. vaga), which are so distinctive a feature of many 

 Naids. Other points in its structure have been already dealt with. The genus Dero is 

 widely distributed like many, if not all, of the aquatic Oligochaeta. It occurs in Europe, 

 North America, the Philippines, Ceylon (if Aulophorus oxycephala of SCHMARDA be really 

 a Dero), and finally, I have received specimens from Mombasa in East tropical Africa. 



The distinction of species is a matter of some difficulty. VAILLANT allows as 

 many as nine ; BOUSFIELD only seven, but this number must be increased by two, 

 for BOUSFIELD was not acquainted with REIGHARD'S observations upon D. vaga, 

 and D. multibranckiata has since been described. Of BOUSFIELD'S seven species, 



Qq 



