292 ClIKSSWELL 8HEAKEH. 



ia tlie family Histriodrilides. In his opinion many of: its 

 characters show its inferiority in organisation to Proto- 

 drilus. Among these the absence of any trace of the 

 circulatory system, the feeble internal segmentation, marked 

 by the complete absence of dissepiments and the small number 

 of segments. On the other hand, the presence of well- 

 developed ganglia points towards a higher organisation than 

 that possessed by any known Archiannelid. Again, the com- 

 plicated sexual apparatus of the male is different from any- 

 thing at present found in this class. The presence also of 

 chitinous jav/s with striated muscles and the anterior and 

 posterior feet he considered as distinguishing it as a type 

 superior to Polygordius. 



More recently Haswell (13) has obtained, as already men- 

 tioned, a freshwater species from the branchial chamber of a 

 Tasmanian crawfish. In the possession of cirri it differs 

 externally slightly from Histriobdella. Haswell pointed 

 out, among other new features, that the lateral organs which 

 Foettinger considered penes are in reality organs that func- 

 tion as claspers, while the penis, as in Dinophilus, is a 

 median unpaired structure. While Foettinger described the 

 seminal vesicles he was unable to trace their ducts to a common 

 receptaculum as Haswell has done in Stratiodrilus. The 

 nervous s^'stem of Stratiodrilus seems to be different how- 

 ever from that of Histriobdella, in being more highly 

 differentiated. In Histriobdella the ventral nerve-cord is 

 still in complete continuity with the epidermal layer, while 

 in Stratiodrilus it is situated much deeper. This difference 

 may be in great part due to the close union of the epidermal 

 and sub-epidermal tissues in contrast to those of Stratio- 

 drilus. A more important difference is the separation shown 

 by the two component halves of the ventral nerve-cord in 

 Histriobdella, and the somewhat different position and 

 number of the ganglia. 



The greatest difference, however, is shown in the excretory 

 system. It is impossible to reduce this to a common type. 

 In Stratiodrilus the crossing and branching of the canals 



