66 Records of the Indian Museum. [Von 
stiffen them) has the systematic value hitherto generally attributed 
tO It. 
The same question is suggested by the fact that the cephali- 
zation is itself a variable feature, sometimes more, sometimes fewer 
segments being so differentiated. Thus, while in most of the 
genera of the Naidide which show this feature the dorsal sete 
begin in segment vi, they begin in ii in Amphicheta, in v in 
Bohemilla. Again, the feature varies within the same genus; in 
Dero some species bear the first dorsal setee on segment v, others on 
vi. Lastly, the feature varies in individual specimens of the same 
species; this has already been stated for the present form; it is 
asserted for Nats communts by Piguet [9]; and it possibly occurs 
in a Slavina, according to my observations {11], though these may 
possibly have been made on specimens which had separated before 
the complete production of their anterior segments in the budding 
zone, and in which possibly the full number would subsequently 
have been formed. 
II.—ON THE REPRODUCTIVE ORGANS OF Nats vartabilis, PIGUET, 
VAR. punjabensis, AND OF Chetogaster orientalis, MIHI. 
The usual mode of reproduction in the Naidide is the asexual, 
by fission. The sexual organs have not hitherto been much used 
in the discrimination of species, and are not referred to in specific 
diagnoses ; they cannot be said to be well-known in more than a 
limited number of species, and in many have not even been seen. 
It is probable, nevertheless, that a fuller knowledge of the sexual 
organs of the Naidide would be of considerable systematic value; 
with regard to the genus Nazs for example, Michaelsen [6] says, 
‘Die bedauerliche Unsicherheit, die noch immer in der Diagnos- 
cirung der Arten des Genus Nazs herrscht, mag meiner Ansicht nach 
am leichtesten durch eine exacte Klarstellung des bisher zur 
systematischen Gliederung dieser Gattung nicht in Rtcksicht 
gezogenen Geschlechtsapparates gehoben werden.’’ The following 
account of the sexual organs of two species, one of them belonging 
to the genus Nats referred to above hy Michaelsen, may therefore be 
useful. 
Nats variabilis, Piguet, var. punjabensis (plate viii, fig. I). 
In a former paper [11] I gave an account of certain features of 
the reproductive apparatus of this form, as far as they could be 
made out by microscopic examination of the living animal. Any 
such account must, however, be very incomplete, since after the 
formation of the clitellum none of the details are any longer 
visible; and, as a matter of fact, I had not then seen the male 
efferent apparatus, which is perhaps the most important part of 
the system for comparative purposes. 
The present description is founded on sections preparéd from 
specimens taken in the Shalimar Gardens, near Lahore, in March, 
