stag*- of completion (tclopliasc, .M. Heidenhain) in which the 

 centrosomes and daughter nuclei assume their normal appear- 

 ance and position in the cells. 



The epoch-making researches of late years (Flemming, M. 

 Heidenhain, Boveri, van Beneden, C. Rabl, v. Kostanecki, etc.) 

 throw clear lights on the mechanism of karyokinesis. These 

 investigations show in the main that the achromatic, part of the 

 karyokinetic figures (radiations and centrosome) form a mechan- 

 ical apparatus upon whose active movements the division of the 

 chromosomes and of the whole cell body depends. The proto- 

 plasmic striations play in this an active role. Their central 

 point of insertion forms the centrosome. 



There arises, then, during karyokinesis under normal con- 

 ditions two nuclei from one, and from each cell two cells. Only 

 exceptionally and mainly under pathological conditions arc many 

 nuclei formed simultaneously by the division of one nucleus. 



The multiplication of cells goes on during the whole life of 

 the organism, so that those cells which under normal conditions 

 must die, may be replaced. 



The duration of life in the cell is variable. Its growth 

 usually goes on as long as life lasts, and the original form of the 

 cell is often much altered. 



Death in the cell is recognized first in the nucleus. Certain 

 changes occur which are spoken of collectively as karyolysu 

 ( ckromatolysis, Flemming). 



For a discussion of endogenous cell division and budding, 

 966 Cartilage and Bone-marrow. 



PROCESS OF FERTILIZATION. 



Division of the egg occurs always after fertilization (parthe- 

 nogenesis excepted). The process of fertilization consists in the 

 conjugation of the male cell (spermatozoon) with the female cell 

 (egg). This leads to the division of the egg, and in consequence 

 the Formation of the embryo. This combination of the sexual 

 cells takes place in such a way that the small and actively motile 

 spermato/oon enters the large and non-motile egg. 



Preceding the fertilization there occur in the egg certain 



