280 CG. CLIFFORD DOBELL. 
the cell—a hypothesis which has been most ably advocated 
by Goldschmidt. This hypothesis of binuclearity,! as 
I shall call it, does not stand alone. There is at least one 
rival hypothesis which also seeks to demonstrate the double 
nature of the cell nucleus. 
Now to comprehend the chromidial hypothesis and _ its 
closely-connected conceptions of binuclearity? it is necessary 
to be familiar with a very large part of the modern literature 
of protistology, and also with much cytological research in 
general; because the branches of the chromidia hypothesis 
have become twisted and tangled among the branches of the 
neighbouring binuclearity hypothesis—so much so, in fact, 
that it 1s nearly impossible to find out where one ends and 
another begins. ‘The only sure way is to trace the offshoots 
from the parent stem. 
It will be my aim in this essay to set out briefly and baldly 
all the main facts regarding chromidia, and to make such 
deductions as seem justifiable; afterwards, to discuss the 
hypotheses based on these facts ; and finally—as this will 
involve a discussion of one binuclearity hypothesis—to criticise 
the other binuclearity hypotheses which are at present often 
confused with the idea of chromidia. ‘To this end I have 
endeavoured to discover and verify facts wherever possible 
for myself. But my main source of information has naturally 
been the immense cytological hterature which has grown 
up in the last few years. From its very size it would, 
of course, be quite impossible to enter into details in a 
short space. But I shall try, by selecting the most impor- 
tant points, to place the essential facts side by side in such a 
way that the value of the hypotheses arismg from them will 
become evident. I wish to show that prevailing opinions are 
' T have used the word “ binuclearity” as an English translation of 
the various expressions commonly used in Germany, e.g. “ Doppelkern- 
igkeit,” ‘‘ Kerndualismus,” “ Kernduplizitat,” ‘“ Kerndimorphismus,” 
“ Binuklearitat.” 
2 Already these hypotheses are occasionally honoured with the 
name of “ theory ”’—and latterly even “law” ! 
