STRUCTURE AND LIFE-HISTORY OF COPROMONAS SUBTILIS. 97 
elucidated, and I am unable to find any proof that the 
zygotes continue to divide like ordinary monads. Teodoresco 
does not appear to have followed out a pair of conjugants 
until the zygote which they produced divided, but he is 
probably correct in supposing that this takes place. “Si cela 
est- vrai,’ he remarks, “ce serait alors le seul cas connu 
jusqu’ a présent @une zygote, provenant de union de deux 
gamétes mobiles, qui dans les conditions favourables de vie, 
ne passerait pas a l’état de repos.” ‘That such a condition 
actually does exist in Copromonas there can be no doubt. 
For, as I have already said, I have watched the living animals 
from the beginning of conjugation to the completion of longi- 
tudinal division in the resulting zygote. 
I have succeeded in following out the nuclear phenomena 
which occur at conjugation in permanent preparations only. 
I will now give the results which I have obtained from a 
study of these preparations, which were made in the manner 
already described (see Pl. 4, fig. 21-33). 
Before conjugation the nucleus appears to be quite normal, 
like the resting nucleus already described. The nuclei of 
both conjugants remain in this state until a considerable 
degree of cytoplasmic fusion has taken place and one 
flagellum has completely disappeared (figs. 21, 22). Hach 
nucleus now divides, going through all the stages which I have 
already described in the process of asexual multiplication. he 
nuclei do not always divide simultaneously (cf. fig. 28). 
Even before division is complete it can usually be seen that 
one of the daughter-nuclei stains more palely than the other. 
This pale nucleus is a reduction nucleus, and it very soon 
degenerates and breaks up. In fig. 24 a pair of conjugants 
are seen in which both the nuclei have divided, so that there 
are now four nuclei present. Of these four, two (the lower 
two in the figure) are reduction nuclei, and may be recog- 
nised by their lighter colour. I should point out that the 
nuclei here appear rather larger than they really are, as the 
specimen has been slightly flattened out on the coverslip. 
So far as I have been able to make out, only one equal 
