Development of the Ovum. Bij W. H. Dallinger & J. Drysdale. 87 
the part of its author to penetrate farther into the matter than his 
predecessors, and by completer knowledge to harmonize or explain 
away conflicting evidence and doubtful interpretation, and if possible 
to give a sequence to the morphological processes in the simplest 
ova, and in the least apparently organized of animal forms. 
From the smallness of the space at our disposal all consideration 
of the second subject discussed in this volume must be passed over. 
It deals with cell and nucleus fission generally ; but as it is chiefly 
theoretical, we may the more readily omit it, merely remarking that 
the author concludes that there is a fundamental harmony in the 
method of fission in the cells of both animals and plants ; a con- 
clusion which it may be fair generally to admit ; but in the minute 
detail, only discoverable by prolonged research, there will be found 
palpable differences. 
That which gives distinction, and to some extent importance to 
the book, is (1) its minute and practical investigation into the 
earliest changes effected by development in the ova of some of the 
more lowly organized animal forms ; and (2) the abundance of data 
which it appears to provide for the support of a new theory of 
propagation amongst the Infusoria, which Biitschli propounds and 
advocates. 
The embryological researches under the first head were con- 
ducted principally upon the ova of the Nematoid worms and the 
Kotifers. To a limited extent the living egg was studied ; but 
the greater part of the results are derived from investigations of the 
ova treated with acetic acid. This is greatly to be regretted. The 
difficulties which present themselves in the minute examination of 
such ova in the living condition, are doubtless great, indeed com- 
plete results could scarcely be obtained from this alone. But 
undoubtedly the continuous examination of a set of living ova in 
process of development should be carried on simultaneously with 
every method of treatment which will reveal structure and change 
in ova of the same form in the dead condition. Only in this way 
can every possible mutation be traced, and its correlation and 
sequence be established. 
It is extremely difficult to distinguish even striking discoveries 
in this direction from the manifold claims put forward by the many 
observers. We must state generally the facts as they at present 
appear, and seek to indicate the points specially claimed as new by 
Biitschli. It is now well known that the ovum is not suddenly 
formed, and then stimulated into new activity by fertilization. It 
evidently, in its very lowliest condition, goes through a process of 
internal growth and development ; after which apparently it perishes 
unless fecundated. In 1864 Balbiani endeavoured to prove that 
besides the germinal vesicle, there existed one still more important, 
which he called the embryogenic cell or vesicle in the ovarian 
