AND ZOOGEOGRAPHY OF INDIAN OLIGOCHjETA. Ill 



Eudichogaster the calciferons glands are in segments x.-xiii., or 



some of them; in Dichogaster as a rule in xv.-xvii. It is not so 

 easy for me as it is for Miehaelsen, apparently, to imagine a 

 "dislocation backwards" of the glands; it is easier for me to 

 conceive Dichogaster arising from Trigaster which has no such 

 glands, than from Eudichogaster which has them, but in a 

 different place. Apart from that, the geographical argument 

 seems to me decisive : Trigaster belongs to Mexico and the West 

 hidies, and these regions are probably part of the endemic home 

 of Dichogaster; Eudichogaster in altogether Indian, and it is very 

 doubtful whether there is any endemic species of Dichogaster 

 in India at all — certainly there is none anywhere near the 

 Eudichogaster region. The place of origin of Dichogaster was 

 pretty certainly not India. I derive Dichogaster therefore from 

 Trigaster. 



Diplocardiincp and Trigastrince. 



There is a line of descent, the Megascolecinae, which leads 

 from the "original Acanthodriline," and in which the initial 

 change is the disappearance of the anterior prostates and the 

 union of the posterior prostatic pores with those of the vasa 

 deferentia on segment xviii. There is another line, the 

 Octochsetinse, in which the initial change is the breaking up of 

 the meganephridia into micronephridia. Similarly, there is a 

 third line, the initial change here being the reduplication of the 

 gizzard. 



This third line (there are still several others) has commonly 

 been divided up into the two subfamilies of the Diplocardiina? 

 and Trigastrinse. These subfamilies, indeed the two combined, 

 are smaller than the Megascolecinse or the Octochajtinse ; 

 the Diplocardiina? comprise only Diplocardia and Zapotetia 

 [Diplocardia having two and Zapotecia three gizzards, a 

 distinction which is not held to be of generic importance in the 

 case of Trigaster, which contains species with both) ; while the 

 Trigastrinse, after the removal of Eudichogaster, comprise 

 Trigaster, Dichogaster, Monogaster, and Eutrigaster (with three 

 gizzards, and three pairs of caleiferous glands in segments xv., 

 xvi. and xvii.). I believe there would be a gain in uniformity 

 and an increase in convenience in uniting the subfamilies under 

 the one head of Trigastrinse. 



" Original Acanthodriline." 

 Diplocardia. 



Zapotecia. Trigaster. 



Dichogaster. 



31onogaster. JEutriffaster, 



