96 Development of the Ovum. Bij W. II. Dallinger dt J. Drysdale. 
ejected organism is assumed to mean nothing? In Blepharisma 
laterita a number of “ nucleolus - like bodies ” were found by 
“ squeezing and acetic acid,” but their destiny was never found ; 
while on the third day after conjugation “ the nucleus which had 
been present up to this time was not to be found,” and so the 
author meets the emergency by supposing that it was “ cast out,” 
and of course had no meaning in the history of the organism. So 
also in Ghilodon cuculus , we are told that the “ destiny of the 
original nucleus remains undetermined.” In the conjugation phe- 
nomena of Stylonichia mytilus there is an equal or even more 
grave defect. 
In precisely the same way in the attempt made by Biitschli 
to establish the position he occupies that the embryonal regions of 
Balbiani and others as existing in these lowly forms are to be 
entirely explained by the presence of swarm-spores of internal para- 
sites, there is the same want of perfect sequence, and the unscientific 
“ no doubt ” which is made to supply the place of facts. 
But our space is exhausted. We have not referred to the above 
defects with any attempt to depreciate a valuable book. It is 
because it is strong enough in important facts to be a help in the 
unravelling of biological difficulties that we have not hesitated to 
point out the difference between the theories and the facts which it 
contains. To have attempted exhaustive criticism of such a work 
would have involved four or five times the space occupied by this 
article ; but after a careful perusal and reperusal of its contents, 
we are obliged to admit the ingenuity of the author both in the 
work he has done and the method he has employed for interpreting 
it. But it is to the former that we attach by far the most import- 
ance ; for whilst there are many missing links in evidence which 
make conclusions from the whole unwise, there are facts given us 
which must help future observers and land us nearer to the desired 
truth. 
It may be finally observed, — 1. That if the theory of rejuvenes- 
cence, as put and insisted on by Biitschli, be established for any 
one form, conjugation should have no other meaning or place in any 
part of its history than rejuvenescence can explain. Now Stylo- 
nichia pustulata is amongst the forms the author has seen to 
conjugate, and as he believes, as a consequence, to become simply 
more vital and larger for renewed fissipartition. But Engelmann 
is undoubtedly right in his affirmation, that there is a conjugate 
state in which these organisms do not again separate, but the pair 
simply fuse together. One of the writers of this paper has observed 
it repeatedly under conditions which render error impossible ; this 
is not the place to consider to what this fusion leads, but it is 
important as a fact, inasmuch as it throws doubt upon the com- 
pleteness of the theory of rejuvenescence, even supposing the facts 
