AND ZOOGEOGRAPHY OF INDIAN OLIGOCH^TA. 139 



thing). But there is no reason to suppose tliat Eupolygaster and 

 Drmvida had a common origin — the reverse in fact ; and if they 

 originated separately, this curious dislocation must have occurred 

 twice independently. 



I believe the explanation to be that the accepted numbering of 

 the segments in Desmogaster is incorrect, and that the numbers 

 given to all the segments should be diminished by one. This 

 view requii'es some justification. 



There are three means of establishing the enumeration of the 

 segments at the anterior end of the body — the set*, which 

 commonly begin in segment ii ; the septa, which are, however, 

 invariably wanting in the anterior segments ; and the annulation 

 of the body. Of the four species of Desmogaster, the setae are 

 invisible in the anterior segments in D. dorice ; they do not begin 

 till segment viii (laterally not till ix) in D. schildi ; they do not 

 begin till segment ix in D. giardi ; and we have no information 

 concerning them in D. horsti, except that they are minute. The 

 setae are thus useless for the determination of segments. 



As to the septa, in all species the extreme displacement of 

 the septa in the anterior part of the body is remai-ked by the 

 authors. In D. horsti the tenth septum (presumably the meaning 

 is septum 10/11) is either absent, or displaced backwards to the 

 level of 11/12 ; if we suppose it to be absent, the numbering of 

 the segments is brought up to that which is generally accepted 

 for the genus, while if w^e make no such supposition, the numbering 

 of the segments is apparently that for which I am contending. 



Concerning the annulation, we only know that in D. horsti 

 "the two antBrior segments have their longitudinal diameter 

 smaller than that of the succeeding ones " — which appears to 

 admit of the supposition that they really constitute a single 

 segment ; and that in D. schildi segments i-iii are simple while 

 iv-xii are biannular. But since there are no setsB near the 

 anterior end of this worm, the distinction of primary and secon- 

 dary grooves is conceivably somewhat arbitrary, and a slight 

 difFei^ence in estimating the value of the grooves would reduce 

 the number of segments by one. It is worth noticing that in a 

 species of Eupolygaster {E. broioni, 13) Michaelsen is in doubt 

 regarding the numbering of the segments because of the secondary 

 annulation, setse being absent here also from the anterior 

 segments. 



Naturally, when the numbering of the segments had once been 

 determined in the first species of Desmogaster (rightly or wrongly), 

 subsequent writers describing new species w^ould, if in any doubt, 

 bring their numbering to correspond, as Michaelsen does in the 

 example of the Eupolygaster just quoted *. 



* The first species of Desmogaster to be described was D. doriee (Rosa, 19). 

 There seem to be inconsistencies in the data there given. The ovaries are said to be 

 in segm. xiii ; but the funnels to be on anterior face of septum 14/15 — i.e., in segment 

 xiv. The spermathecse (there is onlj' a single pair in this species) are first stated to 

 be in viii, but further on to be on the posterior face of septum 6/7 — i.e., in vii. This 

 would seem to indicate that the estimation of the segments was not easy, and that 

 the author himself came to difterent results at different times. 



