AND ZOOGEOGRAPHY OF INDIAN OLIGOOH/ETA. Ill 



Eudichogaster the calciferous 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 Michaelsen, 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 

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

 of Dichogaster \ Eudichogaster xa 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 

 E'ltdichogaster region. The place of origin of Dichogaster was 

 pretty certainly not India. I derive Dichogaster therefore from 

 7'rigaster. 



Diplocardiince 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 

 Octochaetinpe, 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 Diplocardiinse 



and Trigastrinpe. These subfamilies, indeed the two combined, 



are smaller than the Megascolecina? or the Octoch?etinfe ; 



the Diplocardiina3 comprise only Diplocardia and Zapotecia 



[Dxplocardia having two and Zapotecia three gizzards, a 



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



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



Trigastrince, after the removal of Eudichogaster, comprise 



Trigaster, Dichogaster, Monogaster, and Eutrigaster (with three 



gizzards, and three pairs of calciferous 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. 



I 

 Dichocfaster. 



3Iono</aster. Eutrigaster, 



