MITOSIS 101 



karyosomes disappear, and there cannot be detected any structures like 

 centrosomes at the apices of the spindle. When the nuclear membrane 

 commences to divide, karyosomes of the daughter nuclei reappear. 



A modification of the preceding type of division is seen in an amoeba 

 described by Dobell (1914a) under the name Amoeba lacertce. The amceba 

 is a common parasite of the intestine of Lacerta muralis and other lizards. 

 In the resting condition the nucleus consists of a nuclear membrane and 

 large central karyosome, in which all the chromatin of the nucleus is said 

 to be aggregated (Fig. 58). When nuclear division commences, coarse 

 granules of chromatin can be distinguished in the karyosome. These 



•^- *: 



.^ 



■•^^ 











Fig. 58. — Nuclear Division in Valilkampfia dobelli {Amceba lacertm, Dobell, 1914) 

 (x 2,000). (After Dobell, 1914.) 



1. Ordinary form with nucleus containing large karyosome. 



2. Karyosome breaking into granules. 



3. Elongation of karyosome and arrangement of chromatin granules in meridional lines. 

 4 7. Elongation and constriction of karyosome. 



8-9. Comijletion of nuclear division and commencing division of cytoplasm. 

 10. Encysted form. 



become finer and arranged in meridional lines on the surface of the karyo- 

 some, which now becomes elongated, as does also the nuclear membrane. 

 On the surface of the elongated karyosome granules of chromatin are 

 arranged in longitudinal rows, and some indication of fibres can be de- 

 tected. The granules gradually collect at the two poles of the karyosome, 

 which itself becomes constricted at its centre and finally divided into 

 two parts. This is followed by constriction and division of the nuclear 

 membrane, which has persisted throughout the division process. The 

 daughter karyosomes contract to the spherical form, while the granules 

 of chromatin unite to form larger granules. During this division the 



