520 Farmer . — On Spore- Formation and 
as a whole enters the nucleus in this manner. It may well 
happen that the cytoplasm does furnish some constituent of 
that body which we call chromatin in the dividing nucleus, 
but in addition to this there exists another substance which 
forms the essential part of the chromatin, and it seems certain 
that this substance resides in the nucleus. The fact that 
nucleins are not found in the cytoplasm supports this sugges- 
tion. The sudden and large increase in bulk which the 
chromatin exhibits during mitosis is perhaps referable to the 
recombination of the substances which contain phosphorus 
with the albumen, which probably originate from the nucleolus, 
and perhaps partly also from the cytoplasm. 
I have endeavoured in the above discussion to hint at some 
of the lines along which further investigation is much needed, 
and also to indicate the nature of some of the problems which 
await solution. I am conscious that in attempting to touch 
on some of these questions I cannot hope to avoid the charge 
of vagueness. This is, however, unfortunately a defect inherent 
in the present condition of the subjects involved, and I thought 
it best to put forward the difficulties with which I have been 
myself confronted, in order that perhaps others might be 
tempted to overcome them. So little ground has been as 
yet reclaimed, and of that little so much is still unsafe, that 
one can only with diffidence attempt to estimate the general 
bearings of any one set of observations, however true they 
may be for the particular objects investigated. Thus, even 
a short time ago, few would have believed that the achromatic 
spindle could be formed entirely within the nucleus, whereas 
we now recognize that the actual position which it occupies in 
the cell is of no importance from a general standpoint, and in 
the same way many observations which to-day seem to 
possess little significance may prove of considerable value 
to-morrow, as has already happened to the theory of the 
general fusion of the centrosomes during fertilization — 
‘ Multa renascentur quae iam cecidere, cadentque 
Quae nunc sunt in honore 
I cannot do better than close this essay and these reflec- 
