270 Memoirs of the Indian Museum. [Voi,. I, 



I hesitate J however, to describe this second form confidently as P. œquiseta, for 

 the following reasons: This species is described, as indeed is the whole genus 

 (Michaelsen [3]), as possessing only capilliform setse in the dorsal bundles ; there is 

 stated to be only one pair of transverse commissural vessels (Michselsen [3] ; and 

 Beddard [i] ); and the length of the animal is given (Michaelsen [3] ) as 7 — 8 mm. In 

 a later publication [5], however, the latter author brings down the length to 2 — 4 mm., 

 which does not seriously conflict with the description I have given. 



As regards the dorsal setae it is possible, I think, to suppose that the ''needles" 

 described above are in reality hair-setae arrested at an early stage in their growth ; 

 which, so long as their companions are entire, remain in their immature stage, and 

 only receive an impulse to further growth when the accompanying hair-setae fall out. 

 Seeing that, as stated above, I purposely chose only specimens with perfect setae, 

 at least on the third segment, for purposes of description, it would follow on the 

 above hypothesis that I should, as happened, find the second or short setae of each 

 bundle arrested at the stage in which I have described them. 



I cannot, however, reconcile the two descriptions of the commissural blood- 

 vessels. 



Reproductive Organs of Pristina. 



I have grouped together my observations on the genital system of both species 

 of Pristina, because they are few in number, and because probably the anatomy of 

 both is the same ; moreover, I am not quite confident of the species of one or two 

 of my specimens. 



The earliest condition met with is shown in fig. 38. Here there was no clitellum ; 

 the seminal vesicles occupy the seventh and eighth segments, and, though apparently 

 consisting of four separate masses, may be all portions of the same sac. These 

 organs had a hyaline or finely granular appearance, and no distinct cells could be 

 made out. Anteriorly in the sixth segment were a few aggregations of small round 

 cells, possibly developing sperm-morulse. 



In fig. 39 the clitellum has developed over the eighth and ninth segments ; when 

 this has happened, it is impossible by ordinary examination to make out with 

 exactitude the internal anatomy in that region ; the seminal vesicles, however, 

 occupy a large part of those two segments. In segments ix and x is seen an oval 

 mass, pure white in colour to the naked eye, dull and opaque under the microscope 

 by transmitted light, and evidently similar to the mass described [v. ant.) in Nais 

 variabilis. 



In fig. 40, plate xix, the clitellum reaches forwards half way over the seventh 

 segment; a small nodular mass just behind septum 6-7 perhaps represents the testis; 

 the vesiculae séminales extend backwards to the posterior boundary of the ninth 

 segment, and now contain filiform spermatozoa ; a number of sperm masses appeared 

 to be free in the body-cavity in the seventh segment, and at the hinder border of the 

 ninth segment also were two masses of cells which might, from their appearance, have 

 been either young ova or sperm-morulae. The large opaque body occupied segment x. 



