DESCRIPTIONS OF GENERA AND SPECIES 



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Three genera, viz. Tnchochaeta, Pontoscolex, and Geoscolex (possibly also Diachaeta), 

 agree in possessing only a single pair of testes and of ciliated funnels ; there are 

 also in these three genera a single and very long pair of sperm-sacs, especially long 

 and thin in Trichochaeta, Diachaeta, and in Geoscolex forguesi i ; these characters 

 gain in importance from the fact that they occur always together ; that is, there is 

 no genus with elongated sperm-sacs, which has not also the male gonads confined 

 to a single pair ; fm-thermore, the state of affairs is very like what is to be met 

 with in so many of the aquatic Oligochaeta; in the Tubificidae, for example, the 

 testes are but one pair and the sperm-sacs in the same way occupy a large number 

 of segments. I therefore regard this assemblage of characters as defining a central 

 group. It is clear that the genus Onychochaeta comes very near to the genera 

 Trichochaeta, and Pontoscolex, with which it agrees in the usually irregular arrange- 

 ment of the setae, and in the presence of three pairs of spermathecae ; on the other 

 hand, the retractile proboscis of Trichochaeta is a point of affinity with Ithinodrilus, 

 to which genus, excepting in' this character, Anteus comes so near that it is difficult 

 to separate them ; Geoscolex leads towards the second subfamily of the Geoscolicidae, 

 with which it agrees in the ' atrium,' to a less degree in the absence of spermathecae, 

 and in the ventral position of the nephridiopores. In Geoscolex, also, the calciferous 



' A comparatively little known species, possibly referable to a distinct genus (see below;. 



4 M 



