i895. NOTES AND COMMENTS. 377 



multiplying by division, the protoplasm in which these lie is typically 

 a continuous mass increasing by continuous growth. Mr. Bourne 

 lays great stress on recent and beautiful work upon cell-lineage in 

 development. But in most of these cases what has been proved is 

 UHcleav lineage. Hertwig, experimenting with the frog, showed that 

 nuclei could assume different positions in the general mass of proto- 

 plasm under different conditions of development, and we doubt if 

 even the apparent migrations of cells in the development of Nereis 

 necessarily imply more than migration of nuclei. In drawing an 

 argument for the cell-theory from the definite places assigned " cells " 

 in development. Bourne seems to us to have overlooked the experi- 

 ments of Wilson, Driesch, and Hertwig, who have shown that the 

 nuclei may be moved about in the protoplasmic mass almost as 

 freely as " a heap of billiard balls may roll over each other." 



E. B. Wilson's Atlas of Fertilisation" and Karyokinesis. 

 As we have been discussiug the cell, we may refer here to a 

 beautiful Atlas of Fertilisation and Karyokinesis of the Ovum, recently 

 published (price §4 = sixteen shillings), by IMacmillan & Co.'s 

 American house, for the Columbia University Press. It consists of 

 ten plates, each containing four photo-micrographs of stages in the 

 cell-division and fertilisation of the sea-urchin, Toxopneustes vanegatus. 

 The letterpress, in addition to descriptions of the plates, contains a 

 full account of the maturation and fertilisation of eggs, illustrated by 

 drawings partly from preparations of Toxopneustes and partly from 

 other material. The photographic technique was conducted by 

 Mr. Edward Leaming at the Columbia University College of 

 Physicians and Surgeons, while Professor Wilson prepared the 

 sections and preparations, and focussed the apparatus upon the 

 requisite objects. Every biologist owes the greatest gratitude to the 

 authors and publishers of this beautiful volume : and only those who 

 have laboured themselves to make good photographic plates from 

 specimens exhibiting karyokinesis can appreciate the wonderful 

 delicacy of the results. The eggs were " fixed " with a mixture of 

 concentrated aqueous solution of corrosive sublimate (80 per cent.) and 

 glacial acetic acid (20 per cent.) ; and they were stained on the slide 

 with Heidenhain's iron-hamatoxylin. 



It is unnecessary to refer at length to details which every 

 histologist will wish to see himself, and which are too technical for 

 those who are not specialists in histology. Among points of more 

 general interest, we may mention that Professor Wilson accepts the 

 view that a definite number of chromosomes are present in the 

 nucleus of each species. When an egg is preparing to throw off 

 polar bodies, a large part of the chromatin disappears into the "linin" 

 or nucleo-plasm, while tlie remainder appears in half the number of 

 chromosomes normal in the cells of the tissue. Each of these 

 chromosomes is arranged as a tetrad, and when the first polar body 



