1894. CELL-DIVISION. 49 



It has been suggested that the centrosome is formed by a concurrence 

 of two or more of these nucleoli. (2.) Lumps of chromatin which 

 may be numerous, few, or even represented by a single mass. The 

 fate of these structures is quite easy to follow out. They break down 

 to form the chromosomes. (3). The so-called "germinal spots" 

 which exist in the ova of many animals. They maj' be either masses 

 of deeply-staining nuclear substance, with or without vacuoles ; there 

 may be one large germinal spot consisting of two distinct parts, a 

 smaller deeply-staining moiety, and a large, more vesicular portion. 

 The smaller of these nucleoli appear to run together to form one 

 larger one, in which the vacuoles are rhythmically contracting. Thus, 

 in some cases at least, the germinal spot probably acts as an excretory 

 organ to get rid of the waste products of the actively-growing 

 chromosomes. The vacuoles run together into one large one, which 

 then bursts. The whole process has been watched in living eggs, 

 and occupies from four to eight hours for each systole and diastole. 

 What the actual fate of this kind of nucleolus is, is not yet certain, 

 although it has been observed to maintain its individuality for some 

 time after the dissolution of the nuclear membrane. It then suddenly 

 disappears, and is, on this account, possibly to be looked upon as 

 chromatin which has taken on a special function, and consequently 

 become useless as hereditary substance. Hence its apparent dissolu- 

 tion when the nucleus passes into the active condition. 



These, then, are the main facts of Karyokinesis. It is hoped, 

 in a future article, ^ to discuss its important relations to those theories of 

 Heredity which locate the hereditary tendencies in the chromosomes 

 of the nucleus, and also to compare Mitosis with Amitosis, which 

 latter, in all probability, was the most primitive form of cell- division. 



M. D. Hill. 



'^ With that article will be given references to the more important papers bearing 

 on the whole subject. 



E 



