183 
to the spermatozoa, which together with the cementing 
substance make up these bodies. 
An optical longitudinal section of a well-formed sperma- 
tophor of Tubifex rivulorum exhibits the following structure 
(fig. 1, fig. 4): 
Centrally an axial canal, or least refractive portion (@ in 
figs. 4 and 7), probably more or less liquid, which is stained 
by carmine, the rest of the spermatophor being unstained, 
and contains granular matter and shrivelled epithelial cells ; 
this canal runs from end to end, and varies much in width, 
enlarging in the broader posterior part of a large sperm-rope, 
and becoming finer towards the conical head, through which, 
however, it extends, expanding there in conformity with the 
outline. External to this, a dense, highly refringent layer, 
in which a dark line (@) is seen to run ; following this, a less 
refringent striated layer (c), the striz in which are directed, 
when thus seen in optical section, from without obliquely 
backwards (that is, away from the conical head), and towards 
the axial canal. External to the striated layer, we come 
again upon a bright, highly refringent layer (d), which in 
some cases, unless a very good glass is used, appears to 
bound the spermatophor, but there is externally to this a 
fringe (e) of excessively delicate filaments, the projecting 
vibratile portions of the spermatozoa. The extent to which 
these project varies, so that in some sperm-ropes it is difficult 
to make them out at all; in others, they are very obvious. 
In the sperm-rope of 7. wmbellifer they are longer (fig. 14) 
than in 7. rivulorum, and in Liminodrilus and Clitellio they 
are even longer still. But the extent to which they are left 
free must depend very much on the completeness with which 
the spermatophor is developed, on the amount of cementing 
substance, and on its more or less complete condensation. 
This will vary much from time to time, and in different 
specimens. 
The two bright borders d and 6 are due to a peripheral 
hardening of the cementing substance, a more complete con- 
densation at the inner surface where the axial canal is 
excavated, and at the outer free surface. The dark line 4, 
which is sometimes seen very clearly traversing the inner 
bright layer, is interesting as an optical phenomenon, in con- 
nection with the dark line traversing the intermediate 
substance placed between the doubly refracting discs in 
striped muscular tissue, and like it, as explained by Heppner, 
is due-to total internal reflexion. 
Whilst a longitudinal. section may be easily obtained 
through the focussing of the microscope, to obtain a satisfac- 
