HAPLODISCUS PIGEE. 
5 
the organ vary in character (fig. 8, a — c). First are found 
masses of large, finely-granular cells, the nuclei of which are 
evidently about to divide, presenting the appearance shown in 
fig. 8, a. Amongst these are masses, one of which is drawn 
in fig. 8, b, which resemble sperm-morulae, being made up of 
a number of narrow, elongated pieces of protoplasm, each 
piece containing an elongated, deeply-staining nucleus, the 
pieces being spirally grouped around what appears to represent 
the part of the original cell which remains behind after the 
formation of spermatozoa. The elements of the third kind 
(fig. 8, c) are free spermatozoa, which lie loosely in a line 
running from the testis itself to a kind of vesicula seminalis 
at the posterior end of the body. The spermatozoa are elon- 
gated and wedge-shaped, seeming not to be provided with 
vibratile tails. Their nuclei are apparently always elongated 
and thread-like, though in most preparations there are indi- 
vidual examples in which no nucleus at all can be detected. 
The vesicula seminalis is simply a space in the general 
somatic reticulum, a little larger than usual, which is filled 
with spermatozoa ; its size varies according to the sexual 
condition of the animal to which it belongs, but it has not 
seemed worth while to do more than indicate its position in 
the diagram (fig. 10). 
The ductus ej aculatorius appears to open into the 
somatic cavity at a point just ventral to the seminal vesicle. 
It is in the form of a tube, so curved that while its lower half 
is vertical its upper portion and its internal opening look 
directly forwards. Near its external opening, which is situated 
posteriorly in the ventral middle line, the lumen of the duct 
exhibits a considerable dilatation. 
The structure of the walls of the ductus I have not elucidated 
in a satisfactory manner. So far as I have been able to 
determine, it is lined by a thick continuation of the ventral 
cuticle, which, however, exhibits many additional striations 
aud other complications, so as to leave some doubt as to its 
real nature. Outside the cuticle is a layer of large cells, which 
may be either an epithelium or more probably a kind of 
