1gI2.] J. STEPHENSON: Indian Aquatic Oligochaeta. ZOE 
extremely slender extremity are (in preserved specimens) with 
difficulty visible with the ordinary high power, and an immersion 
lens is necessary to appreciate them. These setae are about Iooy 
long, and are closely applied to the proximal part of the shaft 
of the longer seta, the distal curved end of the short seta appear- 
ing to fit round the shaft of the longer. The point of the short 
seta may project slightly above the surface of the body in the 
middle and posterior regions of the animal’s length. 
In the most anterior part of the body, where the gills are 
longest, the setae are entirely enclosed in the gill processes. 
Here each bundle consists of two hair setae, or sometimes of 
only one; if there are two, one is much longer than the other. 
The hair setae are here much slenderer than they are posteriorly. 
This is the condition in the first 12, 13, 18, 26 or 27 gilled 
segments. 
In the next succeeding region of the body the gills are 
becoming shorter, and the hair setae project freely and are no 
Fic. 1.—Branchiodrilus menoni; dorsal needle-seta; x about 375. 
longer contained in the gills. The bundles are composed of one 
hair and one needle. The transition from a thin to a thick type 
of hair seta is marked, and quite sudden. The needle has 
apparently not the typical shape described above ; it is straighter, 
almost or quite without the distal curve, but it narrows rapidly te 
a fine point, like the curved form. 
In the middle and posterior regions of the body the dorsal 
bundles consist of one hair and one needle, of the typical forms 
described above. Occasionally two needles occur in a bundle. 
The ventral setae of the branchial and posterior regions 
of the body may be separated into two forms, though the distinc- 
tion is not a hard and fast one, since intermediate shapes occur ; 
neither is the distribution of the two forms fixed. 
The one form, the more numerous, which may be designated 
the ‘ posterior,’ is distinguished by a comparatively stout shaft, 
often a somewhat greater length, a nodulus distal to the middle 
of the shaft, and by having the prongs of the fork equal in length 
or the distal prong slightly longer (fig. 2). In length they measure 
