356 



PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 



I have borrowed from Parker, figures byCariioy, to illustrate the rest- 

 iiij4' and active stages of the cell, and from Watase, a Japanese student 

 of Clark University, figures representing the high differentiation of 

 the cell contents during division (Figs. 8, 9). They bring out the active 

 and passive elements of the typical cell. 



The phenomena of karyokinesis which attend the division and dis- 

 tribution of the hereditary substance throughout the whole course of 

 embryonic and adult development are well illustrated in Carnoy's fig- 

 ures (Fig. 7). First we have the quiescent period, in which the chro- 



FiG. 8.— Before diviston. Diffehkntiation of 



THE CYTOPLASM AMD Nt'CI-Ers DUIMNG CELL DIVI- 

 SION OF A S(,!UID EJiBiivo. LoLiGO. (After Watase). 

 M, The nuclear iiiembraiio; F, Achromatiu or 

 mirleoplasm : C. Cytoplasm, or Drotoplasin out- 

 side of the iineleus; A -A, The two centro.souies 

 of archoplasiu : B, Extra iiuelear archoplasiuic 

 tilaiueiits; E, Intranuclear arclioplasn ic flla- 

 meiils attached to ti. it', the chromatin rods. 



Fig. 9.— After division. Interior of a daughter- 

 cell IN the syuiD. (After Watase.) Division has 

 just taken jdace and the daiishter nucleus, N, shows 

 the chromatin coil. The daughter ceiitrosome is 

 just forming two new centrosoiues, A-A, by direct 

 division. 



matin ju-esents the ai)i)earaiice of a coiled, tangled thread; surround- 

 ing this is the clear nucleo-plasm (or acln'omatin) bounded by the nu- 

 clear membrane; the extra-nuclear substance, or cyto-plasm, is appar- 

 ently undifferentiated. As soon as cell division sets in, however, ra- 

 diating lines are seen in the cyto-plasm above and below the nucleus; 

 these are called the archo-plasmic filaments by Boveri, since they pro- 

 ceed from what is now believed to be the dynamic element, the archo- 

 plasm (Fig. 8). As the activity becomes more intense the filaments are 

 seen to diverge from a center — the archo-plasmic ce)itro,s<>mc^whk-h lies 

 just Avithout the nucleus at either pole; this radial disi)lay of cell 

 forces suggested the term "asters" to Fol, and ''spheres attractive" to 

 Van IJeneden. The behavior of the chromatin, or hereditary substance, 



