4 
Transactions of the Society. 
rest of the mass, except in the centre, which may perhaps be partly 
due to the organism being slightly concave. It often presents a more 
or less perfectly vacuolated aspect at one or more places, and in any 
position in the head ; in one case it was noticed in the upper part of 
the tail filament, fig. c. 
At such spots, according as they are focused on or into, they may 
appear bright or dark, thus often simulating the appearance of a 
nucleolus if the mass be taken as a nucleus in the original cell — 
Kolliker’s view. Seen on the flat, the anterior edge is often extremely 
delicate, but on the sides and advancing towards the filament the 
boundary is well marked, and after reagents it often shows a double 
outline, which is continued into the neck. The plasm generally 
appeal's to have separated itself into two parts differing in density, 
the separation being marked by a cupped line, or rather giving rise to 
a cupped line, the position of which is not constant, the part near 
the neck being generally the greyest in tint, thus presenting much 
the aspect of an acorn in its cup. I could not find any distinct 
evidence that this cupped appearance was more than optical, and I 
think the proof lies in the fact that this denser or greyish-looking 
part becomes sometimes displaced and occupies the anterior end, 
leaving what would represent the cupped part a perfectly clear out- 
line. This is shown in the fig. e. I am therefore, I regret to say, 
at variance with that excellent observer, Mr. E. M. Nelson. 
The attachment of the head with the filament seems at one stage 
to be continuous, uniform, or jointless, but often at about a distance 
less or equal to the length of the head there is a difference in the tint — 
under different reagents from that given to the rest of the filament — and 
where this ends it often looks as if it were crossed by a line ; and 
when the edges of the filament at this part are slightly enlarged, both 
above and below it, there is the aspect of a joint, and, even at that 
point, often a constriction. 
How seldom, however, is the head seen separated from the filament 
at that point, and this seems to me to militate against the idea of a 
joint, though it very likely is the weak point for separation after 
entering the ovum. Again, if jointed at that point, we might expect 
the filament to be commonly bent there at a right angle ; yet this is 
seldom seen. Often a raggedness or roughness of the edges is noticed at 
the upper part of the filament, the remnant of a nuclear membrane (?). 
Tracing the boundary into the filament, beyond the so-called 
joint, I could detect no true double outline, the slender body present- 
ing the aspect of a flattened, attenuated rod, of very different dimen- 
sions, nor under the most diversified treatment could I detect any 
axial thread or fibrillar division. In some of the preparations, 
especially in those gold-stained, six of the heads showed a dark 
minute point, simulating a nucleolus, but it was so rare when we 
might expect it to be constant, that I am very doubtful whether such 
a definite point may not be accidental, and due to the method pre- 
cipitating a very minute portion of the plasm, or even to the 
