226 NAT URAL SIGLEINIGE Marcu, 
content ourselves with noting a few points. The subject of which 
Professor Hertwig treats is one which the Germans have made par- 
ticularly their own; it is true that eminent persons, not Germans, 
such as Professor Edouard van Beneden, have investigated these 
matters, but the bulk of the work has been done in Germany. 
Professor Hertwig is, of course, a zoologist, but he has by no 
means neglected the botanical side of his subject ; indeed, the work 
would be comparatively valueless if he had. It is one of the most 
remarkable generalisations of Biological science that animal and vege- 
table cells are identical in all important characters. This was first 
realised when the identity of their protoplasm was proved by Von Moh ; 
and the discovery of the nucleus, first due to our countryman, Robert 
Brown, led the way towards proving another fundamental resemblance 
between the structural units of the plant and the animal. Finally, 
the recent discoveries that the phenomena of the dividing nucleus 
termed karyokinesis were not peculiar to the animal cell, but also 
characterised the vegetable cell, left nothing wanting to prove the 
close similarity of the two. There are still remaining certain cells 
in which a nucieus has not been discovered; on the other hand, the 
balance is restored by the existence of other cells which have more 
than a fair share of nuclei. As to the former class, it is doubtful 
whether a nucleus is ever really wanting. The mammalian red blood 
corpuscle will at once occur as an instance of such a cell; but, as 
Professor Hertwig points out, these bodies are not the equivalents of 
cells at all. Some of the simpler amceboid organisms appear to be 
without a nucleus, and it was suggested that in such cases the orga- 
nism was really a free nucleus, with little or no protoplasm. This 
suggestion was made, we believe, by Dr. Will; Dr. Hertwig alludes 
to the matter, but does not quote Dr. Will. The Bacteria are 
organisms whose real nature has been disputed; some have been 
unwilling to allow to these “plants” the rank of a cell. Biitschli, 
however, found deeply staining bodiesin Bacteria to which he assigned 
the value of a nucleus. Dr. Hertwig does not refer in this connection 
—as he might have done—to Mr. Harold Wager’s investigations into 
the nuclei of Bacteria, communicated to the British Association at 
Cardiff. 
An important part of this work deals with karyokinesis. To the 
general account is appended a brief historical sketch of the matter, 
and a discussion of the more debatable points, and among these the 
origin of the centrosoma is the principal one. After giving the argu- 
ments in favour of its nuclear derivation, the author ends with the 
opinion that the time is not ripe for a definite settlement of the 
question. In the current number of the Quarterly Journal of Micro- 
scopical Science is a valuable paper upon these matters. 
An interesting section of the book deals with the position of the 
nucleus in the cell—that is, its relation to growth, deposition of 
‘formed substances,” &c. The nucleus is all-important; a cell, in 
fact, is a territory governed by a despot, the nucleus presiding over all 
the activities of the protoplasm. It was pointed out a few years ago 
that the yolk in the ovum was first formed in the neighbourhood of 
the nucleus, a discovery that entirely does away with a view at one 
time current that the yolk, or, at any rate, a good deal of it, was not 
of home manufacture, but fabricated outside the ovum, and conveyed 
to it through the pores in the egg-membrane. Dr. Hertwig quotes 
and illustrates from the observations of Haberlandt upon the relation 
of the nucleus to thickenings in the cell-wall of vegetable tissues, 
and to the growth in length of cells; when these circumstances are 
