1891.] 



EARTHWORM FROM WEST AFRICA. 



51 



with Levinsen's figure (/oc. cit. pi. vii. figs. 3, 5), the "spear-head" 

 is longer than the shaft. Viewed laterally (fig. 3, a) each seta is 

 seen to be curved from above downwards. Each of these setae is 

 invariably accompanied by an immature seta, the form of which 

 can be understood by reference to the accompanying sketch (fig. 3, c) 

 without any detailed description. 



Fig. 3. 



Genital setae of Sipho nor/aster millsoni. 

 a, seta viewed in profile ; b, ventral view of seta ; c, immature seta. 



Levinsen naturally regards these structures as copulatory organs, 

 but considers that they may also have a respiratory function ; this 

 latter would seem possible on account of their large size and the 

 rich plexus of blood-vessels with which they are furnished. 



The small size of the appendages in S. millsoni is against their 

 performing a respiratory function in that species, but I quite agree 

 with Levinsen in believing that they are in all probability penes. 

 Their position on the body and the spicules with which they are 

 furnished favour this view. 



The genital setae of this Siphonog aster bear a very close resem- 

 blance to the genital setae of Nais elinguis, which have recently been 

 figured for the first time by Dr. A. Stolc^ ; the spear-head form and 

 the proportions between the head and " shaft " appear to be nearly 

 identical in the two forms ; the curvature, too, exists in both, though 

 it is considerably more pronounced in Nais elinguis than in the 

 worm which forms the subject of the present communication. 



This case of an Earthworm possessing setse like those of the lower 

 aquatic forms is very rare ; indeed only one other example is known 

 to me — that is, TJrochceta, in which Perrier first described the 



^ "Prispvesky ku studiu Naidomorpli," SB. bohm. Gesellsch. 1887, p. 227. 



4* 



