STRUCTURE OP TWO NEW GENERA OF EAETHWOEMS. 245 



figured in that drawing appear to be excavated in the substance 

 of cells, wliile there can be no possible question about the 

 ramification of minute tubes. 



One is tempted to regard every ductule excavated in the 

 substance of cells as of nephridial nature, but the origin of the 

 blood-capillaries in the leech by direct canalisation of cells, 

 discovered by Lankester and confirmed by Lang, as well as 

 unicellular glands with a central duct, shows that this conclu- 

 sion cannot be always drawn. 



The study of these oesophageal pouches in Hyperiodrilus 

 is instructive as showing how folds may gradually acquire the 

 character of a system of tubes, and how the subdivision of the 

 tubes, without a corresponding decrease in size of the epithe- 

 lium, may ultimately lead to an intra-cellular network. This 

 series of facts shows also how irrational is the distinction, 

 which some have attempted to draw, between nephridia with 

 an intercellular duct and nephridia with an intra-cellular duct, 

 e. g. between those of the Polychseta and Oligocheeta. 



The tubes are everywhere separated by an abundant plexus 

 of blood- capillaries, which seems to form a continuous sinus. 



In Bucholzia there is a dorsal diverticulum of the oeso- 

 phagus, which Michaelsen has compared with the ventral 

 pouchesof Eudrilus; and in this Enchytrseid the diverticulum 

 is formed of a number of tubules with intra-cellular lumina. 

 § Generative Organs. 



1. Male Generative Organs. — I could only find a single 

 pair of testes; as these were extremely small, it is possible 

 that I may have overlooked the second pair. The pair found 

 were in the 11th segment; each is attached to the vas deferens 

 just where it issues from the septum separating this segment 

 from the one in front. As will be seen later, after the other 

 organs of the male reproductive system have been described, 

 the peculiar arrangement of the vasa defereutia, which are 

 bent upon themselves near to their ccelomic opening, suggests 

 that the missing pair of testes, if they are really present, will 

 be found in the 12th segment. 



The testes of Hyperiodrilus are not enclosed in a special 



