No. 2.] AJVATOMV OF BDELLODRILUS ILLUMINATUS. 517 



large pair of ovarian arches, which are more or less imbedded 

 in the maturing ova, lie in the posterior part of the seventh 

 somite ; and the seventh pair, which are the largest of all, 

 posteriorly connect the supra-neural vessel with the peri-enteric 

 sinus. The walls of the supra-neural and lateral vessels are 

 very delicate and non-contractile. At wide intervals, nuclei, 

 which resemble those of the peritoneal cells, may be detected, 

 but I have found no traces of cell boundaries. 



Nervous sy stein. — The nervous system does not differ in 

 any important particular from the description given by Dorner 

 for Branchiobdella. It consists of a pair of supra-oesophageal 

 ganglia lying just posterior to the dorsal jaw pad. The two 

 ganglia of this pair are united across the median line by a 

 cord of nerve cells and a fibrous commissure ; and each bears 

 well marked posterior lobes, which are themselves divided into 

 larger external and smaller internal parts, and are connected 

 with the main ganglion by three strands of nervous matter 

 (Fig. 17). The vascular arches of the second pair pass along 

 the groove between the anterior and posterior divisions of the 

 ganglia, and follow the connectives about to be described. 

 The circum-cesophageal connectives are thick strands of nerve 

 fibres, with a partial covering of nerve cells which extend from 

 the ganglia particularly along their posterior and anterior 

 faces. They pass around the pharynx, and, just before meet- 

 ing on the ventral side, each bears a bi-lobed pedicled gan- 

 glion (Figs. I and 16), and after uniting to form the ventral 

 nerve cord, two succeeding pairs of similar but larger ganglia ; 

 making in all four pairs of double ganglia within the limits of 

 the head (Figs, i and 16). The nerve cord, which consists of 

 two distinct halves throughout its length, enlarges at the gan- 

 glia and shrinks in the inter-ganglionic intervals. Numerous 

 nerve fibres arise from the circum-oesophageal connectives and 

 the superior ganglia, and pass to the peristomial region. In B. 

 philadelphicus these can be readily traced by the use of methy- 

 lene blue to the circum-oral hairs, and especially to the oral 

 papillae. 



In the post-cephalic somites a ventral chain of eight pairs of 

 bi-lobed ganglia is succeeded by a posterior ganglionic mass, 



