1915.] J. STEPHENSON : Indian Oligochaeta. 39 
Bombay, Poona, and ‘ Sind ’,—each once. Since then I have received a few specimens 
from Baroda (22), as well as those from Bombay recorded below. It is probably from 
this region that we may look for the greatest advance in our knowledge in the future. 
The finding of the first terrestrial species of Pontodrilus is noteworthy. With 
the exception of the lacustrine P. /acustvis (Benham) (described originally as a Plutellus, 
—perhaps its generic affinities are not yet entirely free from doubt, cf. 4 and 11), all 
the previous species of Pontodrilus are littoral ; it is therefore startling to find a repre- 
sentative of the genus living in crevices of quartz many miles from the shore. The 
ancestral Pontodrilus was no doubt terrestrial; and it is interesting to speculate on the 
possibility of P. agnesae as representing that ancestor,—at least in so far as it has 
retained the terrestrial habit, —and of Ceylon as the original home of the genus; 
reaching the shore, and being enabled to adapt themselves to a littoral mode of life, 
its descendants, on this supposition, would have been carried in well-known ways 
widely over the tropical regions of the globe, becoming differentiated into the various 
species which now exist. 
In favour of this, first, is the fact that species of Plutellus, from which Ponto- 
drilus is descended, are endemic in Ceylon. Secondly, the disposition of the seminal 
vesicles in Pontodrilus agnesae {in ix and xii) is peculiar ; those organs in other species 
of Pontodrilus are in general in xi and xii (in P. lacustris in ix and xi). In Plutellus, 
the direct ancestor of Pontodrilus, the seminal vesicles vary in position, but the 
commonest position, which is also perhaps primitive for the Megascolecinae in general, 
is in segments ix and xii, as in the present species.' It is possible therefore that P. 
agnesae tetains a primitive character in the disposition of its seminal vesicles. 
On the other hand P. agnesae shows no trace of a gizzard. Now not only has Plu- 
tellus a gizzard, but certain forms or species of Pontodrilus are also said to possess a 
rudimentary gizzard (though in others it is quite absent). In this feature therefore 
the present species appears to be among those that have departed more widely from 
the parent genus. 
The question is not at present soluble. It is of course just possible that, while 
the littoral species of Pontodrilus may have descended from a Ceylon ancestor repre- 
sented for us to-dayby P. agnesae, and, one step further back, from aCeylon Plutellus, 
Pontodrilus lacustris on the other hand may have originated independently from an 
Australian Plutellus. We are familiar with such parallel developments in the Megas- 
colecidae ; such characters as the perichaetine arrangement of the setae, the micro- 
nephridial condition, the rudimentary gizzard, have arisen at various times in the 
history of the family and on various branches of the tree; so too, according to the 
arguments used in discussing the position of Erythraeodrilus (v. post.), we have in the 
past history of that genus a course of evolution somewhat similar to that which, 
occurring on another branch of the tree, has resulted in Eutyphoeus. 
1 Of the 35 species in which the distribution of the seminal vesicles is mentioned in Michaelsen’s 
Oligochaeta (Tierreich, 1900), they are in ix and xii in 18 ; the next commonest condition is that where 
they occur in xii only (8 species) ; other conditions are represented only by three, two, or one species. 
