DR. NELSON ON THE REPRODUCTION OF THE ASCARIS iMYSTAX. 
565 
which is dilated, and several times the diameter of the testicular tube. Lastly, the 
seminal vesicle contracts slightly and forms the sheath of the spicula (fig. 5 h). The 
membrane forming the csecal extremity (fig. 8«) is very thick but soon becomes 
thin, so that the upper portion of the testicle (fig. 5 o) is perfectly transparent, and 
at the same time homogeneous (fig. 8 5). On examining the membranous walls of 
the generative tube lower down, they first present a granular appearance (fig. 9 5), 
and then longitudinal striae along with the finely granular structure (fig, 10 5). A 
little above the seminal vesicle (fig. bh) the tube becomes muscular, presenting 
transverse rugae (fig. 1 1 ), intended no doubt to force forward the contents. This 
muscular portion, which may be called the vas deferens (fig. 5 m), connects the 
testicle (fig, 5 o, w) with the seminal vesicle (fig, 5 h), and from its contractility 
remains constantly empty and therefore transparent. The vesicle itself (fig. 5 k) is 
covered by reticulations of long muscular fibrillae, giving it the appearance of being- 
enclosed in a net. When these fibres contract, the contained semen must be expelled 
with considerable power. The spicula also are provided with special muscles for 
protrusion and retraction, but into the particulars of these I shall not enter, passing 
to the far more important investigation of the mode in which the seminal particles 
are developed. 
I have already described the apex of the caecal extremity (fig. 8 a) as composed 
of a very thick membrane, but this membrane, although perfectly well defined on the 
exterior is not so within. Externally homogeneous, it becomes internally more and 
more granular till its inner surface appears almost entirely composed of very minute 
granules (fig. 8 c). 
This is the true secreting organ, for the granules when thrown off begin imme- 
diately to swell and form nucleated cells (figs. 8 and 9 d). The homogeneous portion 
of the testicle is filled with little else than these cells of various sizes, floating in a 
transparent fluid (fig. 8), but as it becomes gradually striated, the cells are obscured 
by an immense number of minute opake granules (fig. 9 a), 
The nucleated cells (fig. 9 d) and granules (fig. 9 a) are at first intermixed without 
any order, but further down the granules group themselves round the cells (fig. 9f), 
forming envelopes for each individually (fig. 10 a). On rupturing the testicular tube 
at its commencement, the nucleated cells (Plate XXVI. fig, 18 a) are protruded, 
floating in a granular fluid (fig. 18 5); they have a very transparent cell- wall and a 
nucleus attached to one side (fig. 18 <5). About the middle we find the granular 
masses (fig. 19 a) irregular in form, but within which the nucleated spermatic cells 
(fig. 19 5) may be distinctly seen. The masses are however so delicate that the 
slightest pressure destroys them altogether (fig. 19 c). Passing as far down as the 
muscular portion of the testicular tube, the vas deferens (Plate XXV*. fig. 5 m), we 
find the masses much smaller in size as well as more regular in shape (Plate XXVI. 
fig. 20 a). The granular envelope is globular with a well-defined margin and per- 
fectly opake, so as to render invisible the included cell except when ruptured by 
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