AN ATTEMPT TO CLASSIFY EARTHWOEMS 213 



anterior uephridia for the purposes of alimentation, both for 

 cases where they open into the digestive canal and where they 

 merely open to the exterior, i. e. intra-buccal pepto-nephridia, 

 and extra-buccal pepto-nephridia. 



This modification of the anterior nephridia is also found in 

 some of the families in which large nephridia have replaced 

 the network. In the Geoscolecidee, this is the case : and 

 although in Geoscolex the first nephridium is not very 

 greatly modified, it will be seen to be slightly different from 

 the following ones ; and in fact the coiled tubule is thicker, 

 and is distinctly glandular in appearance. The following 

 ones are somewhat similar. The point of entrance of the 

 tubule into the duct gradually shifts towards the pore, so that 

 the caecum becomes more and more marked. But in the 

 other two genera of the family, Diachseta and Urochaeta, 

 the first pair of nephridia are very different from the following 

 ones, both in regard to their size and complexity, and are 

 " pepto-nephridia." From a glance at the diagrams it will 

 be seen that Diachceta presents an intermediate stage between 

 the more simple condition in Geoscolex and the more com- 

 plicated in Urochaeta. 



Rhinodrilus and Microchaeta also present variations 

 in their nephridia, not so markedly as in the last family, and 

 not so pronounced in Microchaeta as in Rhinodrilus, 

 where the first pair of nephridia are much larger than the 

 following ones, and lie underneath the pharynx. 



In connection with the nephridia it is worthy of note 

 that in Criodrilus and Pontodrilus they are entirely 

 aborted in the first dozen or more somites. Is this con- 

 nected with their aquatic habits ? Is the absence of anterior 

 nephridia analogous to the absence of salivary glands in 

 fishes ? 



The position of the nephridiopore is not in all cases charac- 

 teristic of genera, though this is usually the case. 



The Alimentary Canal. 

 The regions that I have distinguished are — (1) buccal 



