EARLY HISTORY OF THE GERM-NUCUil 



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. 216), 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 (ty:^^ the pri- 

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

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

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

 copepods {CantJiocamptiis, Cyclops) these double rods could be traced 



OZ'."- 



Fig. 136. — Longitudinal section through the ovary of the copepod Canthocamptus. [Hacker,] 



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

 oc. oocyte, or growing ovarian egg; ov. fully formed egg, with double ciiromatin-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 retictibnn formed in tJie gerniiual vesicle (Fig. 136). 

 In the following year Ruckert('93, 2) made a precisely similar discm-- 

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

 of oosconia the daufrhtcr-chromosomes do not give rise to a reticu- 

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

 the entire growth-period of the ^^g. Riickert therefore concluded 

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

 " daughter-spireme of the oogonium {Vr-ei) grown to enormous 

 dimensions, the chromosomes of which are doubled and arranged in 



1 Hacker, Vom Rath, Riickert, in copepods; Ruckert in selachians; Rom and Fick in 

 Amphibia; HoU in the chick; Ruckert in the rabbit. 

 T 



