1908.] J. Stephenson : The Anatomy of some Aquatic Oligochœta. 277 



(2) The suggested sensory function of the dorsal setae of the third segment 



of Pristina Ion gi set a. 



(3) The variations of the length of the prostomium in the genus Pristina, 



and the morphological value of this structure. 



(4) The comparison of the pharynx of Pristina with that of Nais, and 



the conception of the morphology of the septal glands of the former. 



(5) The ''antiperistaltic" action and the reversed ciliary current in the 



intestine of all these forms, and the probable respiratory significance 

 of these. Though the phenomenon of intestinal respiration is well 

 known in the Polychseta, I have not, even in the larger works 

 of reference, found mention of a similar occurrence among the 

 Oligochseta. {Cf., also, its occurrence in a species of Molosoma 

 described by me [g].) 



(6) The concomitance of sexual and asexual reproduction in Nais variabilis ; 



it was formerly stated that these two processes alternate and are 

 mutually exclusive in theNaididse; I have, however, also observed 

 their co-existence in a species of Chcetogaster [q]. Michaelsen [4] 

 has done so in Nais elinguis, and Piguet [7] has observed the same in 

 several forms. 



(7) The ectoparasite of Nais variabilis. 



^OIvOSOMATID^. 

 Molosoma hemprichi, Khrbg. (Pi. xx, figs. 53—55.) 



The following record of the occurrence of this form, not hitherto, apparently, 

 described from anywhere in Asia, may be of interest. The description which follows 

 is fairly full, in order to facilitate more accurate comparisons with the accounts of the 

 species as it occurs in Europe and America. 



The worm is fairly common in stagnant waters in and near Lahore. It will live 

 and multiply under somewhat unfavourable artificial conditions ; thus it was found in 

 numbers in a glass vessel in the laboratory verandah after the summer vacation, and 

 I found it again in the same vessel a few days ago (January) ; the vessel has remained 

 in the same place for six months, the water being occasionally replenished from the 

 tap. Chcetogaster punjabensis was similarly found on both occasions and seems to 

 be equally hardy, and resistant to both heat and cold. A . hemprichi will live a whole 

 morning under microscopic examination, though the water around it may, through 

 inadvertence or otherwise, be suffered repeatedly to evaporate almost completely. 



Its length is on the average about i mm. (-85 — 1-35 mm. extended, as little as 

 •45 mm. contracted). Its diameter varies greatly, according to the degree of contrac- 

 tion or extension, and is usually about -06 mm. Owing to its transparency, it is 

 scarcely discoverable by the naked eye in its usual surroundings, and has to be 

 searched for with a lens. Progression in an anterior direction is a smoothly-gliding 



