AND ZOOGEOGRAPHY OF INDIAN OLIGOCII.ETA. 117 



(using the principle which has in recent years been iUustrated 

 by Dollo and Abel) to a different habit of life, which has left its 

 mark on the race ; that this different habit must have been a 

 life in some other medium than that of water — i.e., it must have 

 been either terrestrial or parasitic ; that the iirst of these is 

 entirely inadmissible, and we are thus thrown back on the 

 second. Also that a number of the other peculiar features of 

 the genus, of which there are many, are explicable in a similar 

 way : and finally that Chcetogaster at tlie present day is still in 

 some cases an ecto- or even an endoparasite (in the pulmonary 

 chamber and liver of fresh- water Gastropods), while in others it 

 is a commensal ; and in still others, though free-living, it (alone 

 among the Naididte, so far as I know) feeds predominantly on 

 a,nimal food *. 



Exactly how or why pn.rasitism should have produced this 

 change in the distribution of the germ-cells, it is not easy to say. 

 Parasitism, of course, places a larger supply of material at the • 

 disposal of the reproductive activities ; but this would not 

 necessarily lead to a different distribution — to a widening or 

 scattering of the germ-track. I can only suggest that there is 

 possibly some connection between past and present habits of 

 nutrition of Ghcetogastei' orlentalis and a change — a scattering — 

 of the germ- track. 



The affinities of the Hirudinea with the Oligochajta have been 

 recognized for some time (compare, for example, the opening 

 paragraph of the chapter on Leeches, by Beddard, in the 

 '■ Cambridge Natural History,' of date 189fi), though text-books 

 still often separate the two groups widely. Thus in the 

 arrangement adopted by Parker and Haswell the Gephyrea and 

 Archiannelida intervene between the Chtetopoda and Hirudinea. 



Michaelsen (2) has recently set forth the evidences for a close 

 relationship between the Oligochseta and the Leeches in detail. 

 The argument rests on the interpretation of certain structures, in 

 Sudanese and Sumatran species of leeches, as spermathecae which 

 communicate with the alimentary canal, — comparable there- 

 fore with those of many Enchyti-asids ; on a consideration of the 

 Branchiobdellidse and of Acanthohdella as intermediate forms 

 (though not necessarily in the direct line of descent of the 

 Leeches); and on the demonstration that there are no pecu- 

 liarities of the organization of Leeches that are not found, or at 

 least foreshadowed, in cei-tain Oligochieta. Detaching the 

 Oligochfeta from their association with the Polychseta in the 



* I raajr mention an additional observation, made since the date of my former 

 paper. I met with a specimen of Chcstogaster orientalis endeavouring to consume 

 a whole Nnis—n. worm about as big as itself ; the end of the Nats had- entered the 

 pharynx of the Ch(etogaster, and I saw it drawn on into tlie region of the crop; the 

 part'of the JVa is outside the C7(«fo5'asie)- was wriggling. On transferring the two 

 animals to a slide thej- unfortunately became separated— the Nais without its head. 

 The ClKBtogaster would not take in the Nais again, though 1 put them in contact 

 several times. 



Kotifers also are a very common food of Chcetogaster orientalis. 



