DR. NELSON ON THE REPRODUCTION OF THE ASCARIS MYSTAX. 
567 
This, then, according to him, is the fully-formed spermatozoon, consisting of a 
spherical cell (fig. \7 o)^ a nucleolus (fig. 17 c), and indistinct nucleus (fig. 17 h). 
This is the substance of previous investigations respecting the development of the 
spermatic particles. I now proceed to state my observations as to their formation in 
the Ascar’is mystax, the phenomena of which will be found to differ materially from 
those just described. 
I have previously stated, that in the more developed condition of the spermatic 
cells they appear as transparent vesicles, without any granular envelope (figs. 21, 
'22 a), but containing a nucleus (figs. 21, 22 b) and nucleolus (figs. 21, 22 c). The 
nucleus appears discoidal when seen from above (fig. 21 b), but lenticular when 
viewed in profile (fig. 22&), apparently enclosed between two portions of the mem- 
branous cell- wall (figs. 22 a and 6?), The internal margin of the nucleus (fig. 22 rf) 
soon loses its clear and defined outline (fig. 23 b ) ; the granular mass constituting 
the nucleus undergoes a marked increase in volume, projecting in a more or less 
conical form towards the centre of the cell (figs. 23-28 b). A membrane is then formed 
over the whole of that part of the nucleus which is in contact with the wall of the 
spermatic cell (figs. 23, 24,/). This membrane is very distinctly seen to separate the 
granular matter of the nucleus from the external cell, with which it is in accurate 
contact. It is also an entirely new formation not to be found in any of the former 
stages, and is apparently produced at the expense of the most external granules of 
the nucleus. The margin, however, of this discoidal membrane (figs. 23, 28 f) is 
not in apposition with the cell-wall, but has a tendency to surround and enclose the 
nucleus ; giving the membrane the form of a watch-glass, whose convexity is in con- 
tact with the spermatic cell, while in its concavity are contained the granules of the 
nucleus, of which it forms a part. The watch-glass form, however, is soon lost, the 
membrane acquiring a tendency to become more convex at its centre, assumes first 
the appearance of a cup, filled to overflowing with the granular substance (fig. 31 f), 
then that of a rounded cone whose margin is everted or bell-shaped (fig. 32 f) ; 
though this is sometimes not to be seen from the nuclear matter which surrounds 
and hides it from view (fig. 33 f). 
When this convexity takes place exactly in the middle, the external cell-wall is 
projected in the form of a papilla (figs. 24 to 27 a), but this is probably only an acci- 
dental occurrence, and not the general rule. 
Although at variance with the statements of Wagner, I say this with the more 
confidence, as Dr. Allen Thomson, with whom I had an opportunity of examining 
these changes, most fully coincides in the view I have here taken. A slight projection 
of the external cell-wall is indeed common at one period ; but in no instance have I 
observed a greater amount of protrusion than that figured in (fig. 27 a). The elonga- 
tion of the nucleus into a tail must be regarded as doubtful in the Ascaris acuminata, 
as it is certainly not the case in the Ascaris mystax. 
