KARYOKINESIS. 47 



role of a semi-permeable membrane and thereby the swelling of the dividing cell is 

 produced which Reinke calls "mitotic pressure." The manner of growth of the 

 nucleus, its turgescence and the infolding of its membrane in the prophase preclude 

 the idea that the nuclear membrane is full of pores as held by Carnoy, Watase, 

 and formerly by Reinke, and indicate that the growth of the nucleus is a phe- 

 nomenon of diosmosis. 



However unequal the division of the cell body may be the daughter nuclei are 

 at first entirely equal, but the subsequent growth of the nucleus is proportional to 

 the quantity of cytoplasm in which it lies; this is shown not only in the cleavage 

 of the egg, but also in the formation of the polar bodies. The nuclei of the polar 

 bodies rarely become vesicular but remain chromatic throughout. The fact that 

 the size of the nucleus is proportional to the quantity of the cytoplasm in which it 

 lies indicates that the achromatic substance absorbed by the nucleus is also propor- 

 tional in quantity to the volume of the cytoplasm. 



It sometimes happens, especially in eggs in which more than the normal num- 

 ber of centrosomes and asters are present, that some or all of the chromosomal vesi- 

 cles do not fuse, but remain distinct through the whole of the resting period. In 

 such cases each of the vesicles behaves like a miniature nucleus, absorbing achro- 

 matic material and forming a network of chromatin either within the vesicle or on 

 its walls, In this growth and differentiation the vesicles keep pace, step by step, 

 with the normal nucleus, so that one must regard the resting nucleus as virtually 

 composed of vesicles, though their union may be so intimate as to hide this structure. 

 The resting nucleus is not, therefore, a single structure anymore than is the equato- 

 rial plate. It is composed of units, each of which, so far as known, has the properties 

 of the entire nucleus, and the union of these vesicles into a single one may be con- 

 sidered as a secondary character. It is altogether probable that the chromosomes, 

 and hence the chromosomal vesicles, preserve their identity throughout the resting 

 period, and I venture the suggestion that the daughter chromosomes will be found 

 to arise within the chromosomal vesicles, as the daughter centrosomes, or centrioles, 

 arise within the mother structures. 



(b) Chromatic Differentiation ; Solution of Oxy chromatin and Nuclear 

 Membrane. — In the early prophase of each division in the mollusks which I have 

 studied, the chromatin becomes sharply differentiated into oxy- and basi-chromatin 

 (Heidenhain). This differentiation occurs before the solution of the nuclear mem- 

 brane, but at a time when the nucleus is growing rapidly in size and is therefore 

 actively absorbing substances from without. This suggests that the rapid absorption 

 of cell substance and the differentiation of the chromatin are associated, but whether 

 this absorption is the cause or the result of the chromatic differentiation, I am un- 

 able to determine. 



The solution of the nucleoli usually precedes that of the oxychromatin 

 spherules and the nuclear membrane, but in the case of the first maturation 

 the enormous nucleolus is thrown out into the cytoplasm before it is completely 

 dissolved. Many oxychromatin granules are not dissolved in the nuclear sap, 



