INDIVIDUALITY OF THE GERM-NUCLEI. 26 1 



In 1883 Van Beneden showed that in Ascaris the sperma- 

 tozoon brings in just as many chromosomes as are contained 

 in the egg. As a result of a careful study of mitosis in 

 epithelial cells of the salamander, Rabl (1885) concluded that 

 the chromosomes do not lose their individuality at the close of 

 division, but persist in the chromatic reticulum of the resting 

 nucleus. Boveri (1887 and 1888) supported Rabl's hypothesis 

 on the ground of his own studies and those of Van Beneden on 

 the early stages of Ascaris. Boveri demonstrated in Ascaris 

 that in the formation of the spireme the chromosomes reappear 

 in the same position as those which entered into the formation 

 of the reticulum, precisely as Rabl had maintained. As the 

 long chromosomes diverge, their free ends are always turned 

 toward the equator of the spindle, and upon the reconstruction 

 of the daughter-nuclei these ends give rise to corresponding lobes 

 of the nucleus, which persist throughout the resting stage. At 

 the succeeding division the chromosomes reappear exactly in 

 the same position, their ends lying in the nuclear lobes as before. 

 These observations were afterwards confirmed by Herla (1893), 

 and more recently Sutton (1902) has observed practically the 

 same thing in Brachystola magna. Boveri (1891) concluded that 

 the chromosomes must be regarded as individuals that have an 

 independent existence in the cell, and expressed his belief that 

 "we may identify every chromatic element arising from a resting 

 nucleus with a definite element that entered into the formation 

 of that nucleus, from which the remarkable conclusion follows 

 that in all cells derived in the regular course of division from the 

 fertilized egg, one half of the chromosomes are of strictly paternal 

 origin, the other half of maternal." 



Herla (1893) and Zoja (1895) have shown that if in Ascaris 

 megalocephala, the egg of variety bivalens, having two chromo- 

 somes, be fertilized with the spermatozoon of variety univalens, 

 having one chromosome, the three chromosomes reappear at each 

 cleavage, at least as far as the twelve-cell stage; and according 

 to Zoja, the paternal chromosome is distinguishable from the 

 two maternal at each step by its smaller size. "We have thus 

 what must be reckoned as more than a possibility, that every cell 



