56 NOTES ON THE ANATOMY OF DINOPHILUS. 



2. Nervous system. — In Protodrilus, as in Dinophilus, ventral 

 nerve-cords run along the sides of the ciliated ventral region of the 

 body. In both cases^ tliese cords are connected with the brain by 

 oesophageal commissures running round the sides of the mouth. 

 Further, the oesophageal commissures in Protodrilus acquire a relation 

 to the longitudinal muscles which is precisely similar to that which 

 obtains, not only in the same region, but throughout the body, in 

 Dinophilus. Protodrilus is well known to possess an almost con- 

 tinuous layer of longitudinal muscles, which are separated by small 

 interspaces into two ventral and two dorsal groups. In the region 

 of the head {v. Hatschek) the four groups of muscles become widely 

 separated; by referring to Hatschek's fig. 14 (Taf. ii), representing 

 a section pasting through the region of the mouth, it will be seen 

 that the ventral longitudinal muscles, in their relative size and in 

 their relations to the oesophageal commissures, are exactly similar to 

 the longitudinal muscles of Dinophilus. Still further forwards in 

 Protodrilus, the dorsal muscles (which do not seem to be represented 

 in Dinophilus) disappear altogether. 



The ventral nervous system of Protodrilus is not known to be 

 segmented, and Hatschek describes only one transverse commissure 

 between the two cords, occurring at the junction of the ''head" 

 and body. 



The researches of Foettinger (2) have shown that Histriobdella is 

 to be regarded as an Archiannelid. Foettinger re-names this animal 

 Eistriodrilus, in order to mark its removal from the group of the 

 Leeches to that of the Archiannelids. 



In one respect, the nervous system of Histriodrilns shows a closer 

 resemblance to that of Dinophilus tseniatus than is manifested by 

 that of any other Archiannelid. The ventral nervous system has 

 been shown by Foettinger to be definitely segmented, in correspond- 

 ence with the external segmentation indicated by metameric con- 

 strictions of the skin. Histriodrilns possesses about eight ventral 

 ganglia, which, however, differ f lom those of Dinophilus in being con- 

 tinuous across the middle ventral line. In the intersegmental regions 

 alone, the ventral nervous system consists of separated ventre- lateral 

 cords. Paired oesophageal nerves, similar to those of Dinophilus, 

 are described and figured by Foettinger (pi. xxv, figs. 10, U). 



3. Excretory and generative organs. — The nephridia of D. tseniatus 

 closely resemble those of Protodrilus, as described by Hatschek. 

 According to this observer, each nephridium of Protodrilus commences 

 with a small funnel, opening into the body-cavity, and bearing 

 internally a single, very long ciliutn. The difficulty of the investi- 

 gation of nephridia of this type makes it possible that the difference 

 between the funnel in Protodrilus and the ciliated appendage in 



