THE CENTROSOME AND THE BLEPHAROPLAST 



77 



receive consideration in the chapter on the achromatic figure. 1 Very 

 often there are two centrosomes lying side by side in the centrosphere, 



FIG. 18. Centrosomes in animal cells. 



A, attraction sphere above nucleus in spermatoeyte of Salamandra. (After Rawitz; 

 see also Fig. 59.) B-F, intranuclear centrosome in spermatoeyte of Ascaris megalocephala 

 and its behavior during the prophases of mitosis; c, centrosphere; chr, chromosome tetrad. 

 (After Brauer, 1893.) 



the two having arisen by the division of one, apparently in preparation 

 for the next cell-division (Fig. 19). Von Winiwarter (1912) noticed 

 that in interstitial testicular cells, which may 

 have one, two, or four nuclei, there are re- 

 spectively two, four, and eight rod-like cen- 

 trosomes lying in midst of a granular mass 

 ("idiosome"). In some cells there may be a 

 larger number of smaller "centrioles" rather 

 then one centrosome, and occasionally there are 

 one or more concentric series of granules about 

 the central centrosome. Several such types 

 described by various writers are shown in 

 Wilson's Fig. 152. It is questionable how far 

 these are normal appearances, for Chambers 

 (1917) asserts that several of them may be pro- 

 duced in the animal egg by subjecting the latter 

 to abnormal environmental conditions. 



Individuality. The centrosome was dis- 

 covered and described by Flemming (1875) 

 and independently by van Beneden (1876). In 

 1887 van Beneden and Boveri, as a result of 

 their researches on the thread- worm, Ascaris 

 megalocephala, independently concluded that the 

 centrosome, like the nucleus, is a permanent cell 

 organ maintaining its individuality throughout 



FIG. 19. Centrosomes in 



epithelial cells. 

 A, from cornea of mon- 

 key. B, from gastric gland 

 of man. (After Zimmer- 

 mann.) 



1 Because of the relation of the centrosome to the achromatic figure it will be 

 necessary to make constant reference to the latter. Chapter IX should be consulted 

 in this connection. 



