200 W. BLAXLAND BENHAM. 
walls, upon which are greatly convoluted and contractile 
commissural blood-vessels. 
These sperm-sacs are asymmetrically arranged. There is 
usually one in Segment 1x, and another starting in Segment x1, 
and extending back as far as Segment xiv or xv, pushing the 
intervening septa in front of it. Very usually, though I 
believe not invariably, this sac crosses from one side of the 
body to the other dorsally of the gut. 
Besides these two sacs (Claparéde’s “ testicles’’) masses of 
developing spermatozoa more or less fill Segment x. The 
minute structure of various parts of the male apparatus 
deserves a brief description, not from any peculiarity special 
to the genus, but because we have but few details of the 
histology of these aquatic Oligochetes. The figures of 
Claparéde, Vejdosky, Hisen, &c., are, in the main, some- 
what diagrammatic, even where these authors intend to show 
detailed structure. Beddard has recently contributed some 
facts as to the minute structure of Hemitubifex and 
Phreoryctes, and Michaelsen has recorded something of 
the histology of Enchytreids. 
The sperm-duct, when its surface is viewed, is seen to be 
striated transversely, as is the case in Tubifex, &c. The 
minute structure, as seen in sections, is exhibited in my 
fig. 23, which includes a transverse and a_ longitudinal 
section of the sperm-duct. 
In transverse section there is a remarkable “ striation” of 
the wall, which is apparently due to radial arrangement of the 
granules in the cells ; this is seen even better in a series stained 
in hematoxylin than in the borax-carmine sections drawn. 
IT can see no boundaries to the cells; and the nuclei are not 
elongated radially, but tangentially : they are, in fact, ovoid in 
shape, the long axis being at right angles to the axis of duct, 
so that in longitudinal section the nuclei have circular out- 
lines. I have seen a similar arrangement in Tubifex, both 
as regards striation and nuclei. 
In earthworms, e.g. Lumbricus, Pericheta, the stria- 
tion is present, but the nuclei appear to be spherical, giving a 
