14 EARTHWORMS AND THEIR ALLIES [ch. 



In all essentials however the two types agree and 

 are thus to be looked upon as referable to the same 

 genus. Starting from the structure of these types we 

 may now sketch in quite a brief way the main 

 divergencies of structure shown in the group of 

 Oligochaeta. 



We shall naturally begin with the family Megasco- 

 lecidae of which a type has just been described. 



Within the limits of the same sub-family as that 

 which contains Notiodrilus, i.e. the Acanthodrilinae, 

 the changes of structure affect all the principal organs 

 of the body except the nervous system, but are not 

 very large and vary from genus to genus. They are 

 mainly perhaps in the direction of reduction and 

 simplification. Thus in Chilota, Maheina and Ya- 

 gansia the spermaries are reduced to one pair in 

 either the xth or xith segment, while in Yagansia 

 one pair of spermathecae and of spermiducal glands 

 have also disappeared. In Microscolex the sper- 

 maries remain normal, but one pair of spermathecae 

 and of spermiducal glands have disappeared, the 

 remaining organs of these series being in the ixth 

 and xviith segments respectively. In Microscolex, 

 Chilota and Yagansia, moreover, there is a further 

 degeneration in the disappearance of the calciferous 

 glands. These glands are often absent and sometimes 

 less developed in the New Zealand MaoridHlus, 

 which is otherwise not a degenerate form and differs 



