226 NATURAL SCIENCE. March. 



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 theidentityof their protoplasm was proved by Von Mohl ; 

 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 nucleus 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 amoeboid 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 bodies in 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 



