D. L. MACKINNON 
forms as degenerate, and without any sex significance. I see that 
Berliner (1909) also interprets as degenerate similar flagellate individuals 
of Herpetomonas jaculum, Leger. I must admit, however, that on two 
occasions I met with appearances in my Giemsa-stained material that 
might be looked on as the beginning of conjugation of male and female 
individuals. Fig. 20 shows such a case. The large half-encysted 
individual, with pale-blue vacuolated protoplasm, the kineto-nucleus 
indistinguishable from other darkly-staining granules in the cell, and 
with the tropho-nucleus situated to one side and apparently extruding 
chromatin, might be the female, while the small flagellate form along¬ 
side, without tropho-nucleus, and with its cytoplasm staining pale-pink, 
might be the male gamete. On the other hand, the juxtaposition of 
these apparently sexual individuals might be mere chance. If con¬ 
jugation be a regular occurrence in this group of flagellates, it is at least 
surprising that we have hitherto had so little convincing proof of the act 
itself. Authors who arbitrarily fix on “ male ” and “ female ” characters 
do not give sufficient consideration to the effects known to be produced 
in protozoa by periods of long continued multiplication 1 . Nuclear 
hypertrophy, nuclear absorption, the production of undersized individuals, 
and the suppression of cell-division, resulting in the formation of 
abnormally large individuals, are all well-known signs of degeneration 
in protozoa, and have to be reckoned with. It is true, of course, that 
conjugation may be resorted to as a means of restoring the karyoplasmic. 
equilibrium, but I hold that in the case of the herpetomonads and their 
allies, we have insufficient proof of this. It should be remembered that 
encystment is another process that may be made use of by protozoa for 
self-regulation after periods of prolonged multiplication and consequent 
depression. This regulation may be effected by extrusion of chromatin 
1 In Hindle’s recent very interesting work (1909) on Trypanosoma dimorphon, lie 
tentatively distinguishes, on morphological grounds, male, female, and indifferent forms. 
It is interesting to notice that the “female” is formed from the “indifferent” trypanosome 
by a process strongly suggestive of the beginning of cell degeneration. The sluggish 
movements, “stumpy” form, very dense protoplasm containing chromatoid granules, the 
very large, densely-staining tropho-nucleus, and the frequent extrusion of chromatin from 
the nucleus, are all features that one is accustomed to associate with cell degeneration. 
Further, these forms do not occur during the earlier stages of the attack ; that is to say, 
they appear only after the organism has been multiplying by division for some considerable 
time, and when we might reasonably expect to find some sign of “depression.” Hindle 
himself states that these “female” forms may be found “in all stages of degeneration” in 
the blood of the rat, but he evidently considers that this would not occur if the conditions 
were favourable for conjugation: such conditions he thinks might be offered by an 
intermediate host. 
