EARLY HISTORY OF THE GERM-NUCLEI 



273 



nection with the reduction-problem ; and some of these have raised 

 some remarkable questions regarding the origin of reduction. A 

 large number of observers are now agreed that during the growth- 

 period preceding the maturation-division (p. 236), in both sexes, the 

 nucleus of the mother-cell (spermatogonium, oogonium), both in 

 plants and in animals, passes through some of the changes prepara- 

 tory to reduction at a very early period. Thus, in the egg the pri- 

 mary chromatin-rods are often present in the very young ovarian 

 eggs, and from their first appearance are already split longitudinally. 1 

 Hacker ('92, 2) made the interesting discovery that in some of the 

 copepods (CanthocamptuS) Cyclops) these double rods could be traced 



Fig. 136. Longitudinal section through the ovary of the copepod Canthocamptus. [HACKER.] 

 og. The youngest germ-cells or oogonia (dividing at og.' 2 ) ; a, upper part of the growth-zone; 

 oc. oocyte, or growing ovarian egg; ov, fully formed egg, with double chromatin-rods. 



back continuously to a double spireme-thread, following immediately 

 upon the division of the last generation of oogonia, and that at no 

 period is a true reticulum formed in tJie germinal vesicle (Fig. 136). 

 In the following year Riickert('93, 2) made a precisely similar discov- 

 ery in the case of selachians. After division of the last generation 

 of oogonia the daughter-chromosomes do not give rise to a reticu- 

 lum, but split lengthwise, and persist in this condition throughout 

 the entire growth-period of the egg. Riickert therefore concluded 

 that the germinal vesicle of the selachians is to be regarded as a 

 " daughter-spireme of the oogonium ( Ur-ei) grown to enormous 

 dimensions, the chromosomes of which are doubled and arranged in 



1 Hacker, Yom Rath, Riickert, in copepods; Riickert in selachians; Born and Fick in 

 Amphibia; Hull in the chick; Riickert in the rabbit. 



