218 OLIGOCHAETA 



Genus PHBEATOTHRIX, VEJDOVSKY. 

 Syn. Trichodrilus, VEJDOVSKY. 



DEFINITION. Setae sigmoid, not uncinate ; one pair of spermathecae in XI. In 

 posterior region of body, five or six pairs of lateral contractile branches of dorsal 

 vessel in each segment. 



This genus, first described by VEJDOVSKY as a species of Trichodrilus, was 

 subsequently (24) recognized as a distinct genus. Our knowledge of its structure is 

 entirely due to VEJDOVSKY. 



The reproductive organs are like those of Trichodrilus, except for the fact that 

 there is only a single pair of spermathecae lying in the eleventh segment ; in the 

 twelfth segment, however, a rudimentary second pair make their appearance, but only 

 acquire traces of a lumen, and finally completely degenerate. The external orifices of 

 the spermathecae lie behind the ventral setae 1 . There is no albumen-gland. 



The nephridia are very remarkable ; the first pair appears to belong to the eighth 

 segment; the funnels open into the coelom of the seventh segment, and the external 

 pore of the organ is upon the eighth segment ; but the tube which connects these 

 two openings extends back through the body as far as the fourteenth segment. The 

 second pair of nephridia is similarly elongated. The funnels open into the thirteenth 

 segment, and the external pores are upon the fourteenth segment. The tube is looped 

 back as far as the twenty-first segment. Behind this, each pair of nephridia extends 

 through three segments, although, as before, the internal and external apertures are 

 upon successive segments. 



The principal point of interest in the circulatory system is the condition of 

 the characteristic appendages of the dorsal vessel. There are in the posterior 

 segments of the body five or six pairs of these to each segment, which are not 

 regular in their arrangement ; each of these branches terminates in a bifid extremity. 

 The blood is described by VEJDOVSKY as being yellow rather than red. There are eight 

 pairs of perivisceral vessels uniting the dorsal and ventral trunks in the anterior 

 segments. The ventral vessel is forked in the fourth segment. In the young worm 

 septal glands can be made out in the anterior segments. There are four pairs of 

 these lying in segments iv-viii ; the glands of each side of the body are connected by 

 a longitudinal strand, which is the duct, and which opens into the pharynx. They 

 are not so plain in older worms. 



1 In VEJDOVSKY'S first account of the anatomy of this species (21) the setae of this segment are stated 

 to be absent. 



