DIV. I MORPHOLOGY 23 



as the daughter chromosomes in order to form the daughter nuclei 

 (10-12 /). During this stage (diaster) the chromosomes are as a rule 

 U-shaped with the bends towards the poles of the spindle. Having 

 reached the poles they crowd together, while the surrounding 

 cytoplasm forms the nuclear membrane delimiting the new nuclei. 

 Within the latter the chromosomes again assume a reticulate 

 structure (11) and unite with one another to form a network (12), 

 within which their individual limits are not distinguishable. We are 

 compelled, however, to assume that the individuality of the chromo- 

 somes is not lost. The young nuclei enlarge and one or more nucleoli 

 again appear within them (12). 



The end attained by this mechanism of division is that the 

 substance of the ^nucleus, and especially of the chromosomes, is dis- 

 tributed as equally as possible to the two 

 daughter nuclei at each division. From this 

 it may be concluded that the chromatin is 

 especially important for the life of the cell and 

 of the whole organism, and that the chromo- 

 somes play the main part in the transmission 

 of hereditary qualities. 



The number of chromosomes occurring in 

 any nucleus is a definite one, and when a 

 deviation from the usual number is met with, FlG - u. Young ceils from a 

 it is due to some of the chromosomes having 1""^ 

 remained united end to end ( 21 ). The chromo- showing a nuclear plate in 

 somes of a nucleus may be of different sizes the P olar view - The chr0 ' 



/T ,. , . v , i i-rt mosomes are grouped in 



(Fig. 14) ;^ when such differences in size exist ^^ (x 160C . AfterSxRAs- 



they persist in successive divisions. The BURGER.) 



smallest number of chromosomes which has 



yet been found in the nuclei of vegetative cells of the more highly 



organised plants has been six ; as a rule the number is much larger. 



In the lowest divisions of the vegetable kingdom, in some Algae 

 and Fungi, the process of indirect nuclear division is simplified, the 

 masses of chromatin being less carefully divided between the daughter 

 nuclei ( 13 ). 



The changes occurring in a mother nucleus preparatory to division are termed 

 the PROPHASES of the karyokinesis. These changes extend to the formation of the 

 nuclear plate, and include also the process of the longitudinal division of the chromo- 

 somes. The stage of the nuclear plate is the METAPHASE. The separation of the 

 daughter chromosomes is accomplished in the ANAPHASE, and the formation of 

 the daughter nuclei in the TELOPHASE of the division. The real purpose of the 

 whole process is attained in the quantitative and qualitative division of the 

 chromosomes, resulting from their longitudinal splitting. The anaphases and 

 telophases of the karyokinesis are but a reverse repetition of the prophases. The 

 reversal of the stages in the process of nuclear division commences with the 

 separation of the daughter chromosomes. The stage of the nuclear plate at 



