576 
DR. NELSON ON THE REPRODUCTION OF THE ASCARIS MYSTAX. 
period of an oblong shape (Plate XXVIII. fig. 58), and appears to be entirely made 
up of distinct opake granules, which completely hide the germinal vesicle and spot 
(figs. 58 to 60 c). 
The edge at first is uniform, that is to say, not ragged, but presents a distinct 
outline (fig. 58 d). Sometimes a faint trace of the germinal vesicle may be perceived 
(fig. 60 h), although the ovule is never so transparent as to allov^ objects on the other 
side to be seen through it. 
In the upper portion of the oviduct (Plate XXVII. fig. 42 «) we find the spermatic 
particles (fig. 42 jo) in their greatest perfection (Plate XXVI. fig. 38 g), presenting the 
flask-like appearance, and in such numbers as to fill all the interstices between tlie 
ovulum and the sides of the oviduct. 
At first the margin of the ovule (Plate XXVIII. fig. 51c?) is entire, that is to say, the 
clear substance presents a distinct, even and continuous surface, but a little further 
we perceive the spermatic particles to be closely applied against the ovule, depressing 
its surface in some places (fig. 60 g). Another step in advance, and all the ovula 
present an irregular rupture in some part or other of their periphery (figs. 58 to 60), 
generally at one side (fig. 58), and frequently in several places at the same time 
(figs. 59, 60). 
Dr. Allen Thomson, having frequently examined these appearances, permits me to 
say that he agrees entirely with the above description of the phenomena. 
That these appearances do not arise from pressure applied during the examination 
I am perfectly satisfied, having repeated my observations above a hundred times, 
and varied them so as to remove all possibility of such an occurrence. The effect 
of pressure on the ovule is also very different from that just described, as I have 
repeatedly seen ; for if an entire ovule be squeezed between glasses, the vitelline 
granules coalesce, the clear substance dilates, and at last the whole lapses into a 
yellowish fluid. 
From the immense number of ovula in which I have seen this partial rupture of 
the vitellus, and the want of success in my endeavours to cause a similar protrusion 
(figs. 58 to 60 c) of the yolk-granules by compression, I am irresistibly led to the con- 
clusion that this is a vital phenomenon consequent on some natural cause, and not 
the l esult of accidental violence. Further, to make all certain, I divided the oviduct 
at both ends, washed away all loose ovules by a gentle stream of water, and then su- 
perimposed, as carefully as possible, a piece of the thinnest glass. No other pressure 
than the weight of the thin piece of glass was applied, yet every one of the ovules, as 
they slowly found their way out of the oviduct, presented in some part or another 
this rupture of the surface. 
The reason why all the granules do not escape, arises from their being imbedded, 
not in a fluid, but in a sort of gelatinous substance, easily broken up, it is true, but 
sufficiently coherent to retain the granules in their places. 
To what then are these appearances owing, and how are they produced r I have 
