Later Spermatogonial of Fasciola hepatica. 73 
body, there being no crisp distinction between the chromatin and the rest 
ef the nucleus. One or two plasmosomes may be present. As preparation 
for prophase begins the chromatin condenses out into a network of fine 
threads which anastomose in all directions, the nucleus meantime becoming 
larger (PJ. III. fig. 2). 
N.B.—In a rapidly developing tissue such as is presented in the gonad 
of Fasciola there is, practically speaking, no true resting nucleus stage. In 
the present account the term resting nucleus is merely used to designate 
one of the many stages occurring between the more obvious telophases 
and prophases. 
In Fasciola very early prophases can always be distinguished from late 
telophases by the purity of the colour assumed by the chromatin. The 
chromatin has a fresh-looking appearance which contrasts with the some- 
what muddy colour it assumes in the older phases. 
It is impossible to count the prophase threads at this stage (Fig. 2). 
Finally the threads thicken, shorten, and le under the nuclear membrane, 
which, as is usual, is very much distended by the increasing volume of 
nuclear sap (Figs. 3-5). It is difficult to show twenty-four of these 
chromosomes in a drawing of a single prophase, but in most cases it is 
possible to count them. There is a difference in size, some being longer than 
others, but they are characteristically somatic-like, 2.¢. are simple, short, rod- 
like bodies—the rings, crosses, etc., of the meiotic prophases being absent. 
As prophase merges into metaphase (PI. IIT. fig. 6) the chromosomes become 
agoregated towards the centre of the cell, finally becoming so massed together 
that it is quite impossible to count them. In this respect the spermatogonial 
metaphase is very different from that of the spermatocyte I. in which the 
twelve bivalent chromosomes stand out in diagrammatic clearness (Fig. 34). 
As an instance of this tendency to dense massing in metaphase, in many 
studies of equatorial plates of the last two spermatogonial divisions, no more 
than from twelve to fifteen chromosomes could be counted, and this in 
sections where the Flemming fixation was exceptionally good. This fact 
may probably account for the discrepancy in the number assigned by different 
workers on Fasciola (Distomum) as the somatic number of chromosomes. 
In metaphase the shape of the cell begins to change, and a longitudinal 
splitting of chromosomes can sometimes be witnessed. In anaphase the 
chromosomes separate off to either side, but the chromatin mass is again 
too dense for counting chromosomes (PI. III. fig. 7). The spindle apparatus is 
exceedingly ill defined—the two daughter masses forming a cap for either 
end of the mother cell. When they separate, the newly-formed nuclei of 
the daughter cells, on account of this cap-like arrangement, might easily be 
