AM) ZOOGEOGRAPHY OK INDIAN OLIGuCH^TA. 105 



primary characteristic, is the splitting up of the nephridial 



system. 



Original Acanthodriline 

 (single gizzard; meganephridia ; 



no calciferous glands). 



Octochcetiis Diplocardia 



(single gizzard; micronepliridia ; (double gizzard; meganephridia; 

 calc. glands in xv. or xvi. in most no calc. glands), 



species). 



Trigaster * 

 (double or triple gizzard ; 

 micronepliridia ; no calc. glands). 



Dichogaster 

 (double gizzard; micronepliridia; 

 calc. glands in region xiv.-xvii.). 



Eudichog •aster, whose position is now under discussion, has a 

 double gizzard, is micronephridial, and has calciferous glands 

 (except in one species) in two or more of segments x.-xiii. ; in 

 some species the posterior male organs have undergone the 

 microscolecine reduction. It is purely Indian in distribution. 



The view, now held by Michaelsen, that Eudichogaster is derived 

 from Trigaster, and therefore to be included in the Trigastrinae, 

 is based primarily on the close anatomical similarity between 

 the two genera ; the only essential difference is that calciferous 

 glands are absent in Trigaster and present in Eudichogaster. 

 Moreover, there is one species of Eudichogaster in which calciferous 

 glands can scarcely be said to be present at all. Michaelsen, 

 in describing E. bengalensis (5) says : — " a pair of lateral 

 calciferous glands in each of segments x.-xiii., not externally 

 demarcated." In giving additional notes on the same species (9) 

 I have stated that " the bulgings of the oesophagus in segments 

 x.-xiii. are thin-walled and are not at all set off from the lateral 

 walls of the oesophagus ; they are not calcareous glands any more 

 than the similar part of the tube in, for example, Pheretima 

 posthuma is a series of calcareous glands " ; and in support there 

 follows a description of the appearances seen on opening the 

 tube. Here, then, is a form which according to strict definition 

 is a Trigaster ; though 1 imagine no one will quarrel with either 

 MHiaelsen or me for including it, on geographical grounds, in 

 Eudichogaster. 



Michaelsen also regards the similarity of the nephridial 

 condition as being decisively in favour of the derivation of 

 Eudichogaster from Trigaster rather than from Octochcetiis. The 

 species investigated for the purpose of this comparison were 

 Eudichogaster ashworthi, Trigaster lankesteri subsp. calwoodi, 

 and Octochcetas thurstoni. In Eudichogaster ashworthi there 

 occurs in each segment a number of small loose micronephridial 



