5IO The Ohio Naturalist. [Vol. XV, No. 7, 



division in the first reduction karyokinesis was again reported 

 essentially similar to that described for Lilium philadelphicum. 

 At the time this paper was written, the writer still knew nothing 

 of Mendelian heredity. The following statement was made in 

 regard to the probable individuality of univalent chromosomes in 

 the bivalent chromosome — "Altho there is no way known to the 

 writer of tracing the origin of the reduction chromosome in this 

 nucleus to two previous ones, theoretically one might consider it pos- 

 sible that the reduction chroinosome represents two nonnal chromo- 

 somes, and the closed loop the point where the usual transverse 

 break should have taken place." Namely, when the double num- 

 ber of chromosomes are formed from the continuous spirem. 

 "But such a process would necessarily result in a qualitative 

 division." 



That the bivalent chromosome is actually made up of a pair 

 of univalents, one from the maternal and one from the paternal 

 side, was definitely shown to be the case by Montgomery* 

 in 1904. Thus the general facts of the reduction division had 

 been worked out and there was only needed a comparison of the 

 results with the rediscovered Mendelian heredity. Such coin- 

 parisons were of course, made by many writers. 



The cytological evidence may be summarized as follows: 

 the chromosomes are self-perpetuating bodies which have a defi- 

 nite individuality of size and shape which can be recognized in 

 many species. This individuality is not lost or impaired when 

 the chromosomes spread out in the form of a network in the 

 resting nucleus nor when they join end to end to form a con- 

 tinuous spirem. The haploid number of chromosoines represents 

 a nonnal complement or set, each of which developes a specific 

 attraction and unites with its corresponding or synaptic mate 

 in the prophases of the reduction division (synapsis period) 

 and each pair is segregated according to the law of chance to 

 the two poles of the spindle. When at a future period gametes 

 are formed and fertilization takes place, the univalents do not 

 fuse but retain their separate existence during the entire z}'gotic 

 stage of the organism. The pairing of corresponding univalents 

 is of fundamental importance; for without such a process heredi- 

 tary ratios would be much more complicated than what they 

 really are, even tho the reduction division ])rocccdcd normally. 

 The chromosomes representing synaptic mates may have absolute- 

 ly similar hereditary factors and thus be homozygous and the 



4. Montgomery, Jk. T. H. vSome Ob.scrvations and Considerations 

 upon the Maturation Phenomena of the Germ Cells. Biol. Bull. 6: 137-158. 



See also Montgomery: The Spermatogenesis of Peripatus (Peripatop- 

 sis) balfouri up to the Formation of the Spermatid. Zoolog. Jahrb. 14: 

 1900 and Montgomery; Mitosis in Amphibia and its General Significance. 

 Biol. Bull. 4: 259-269, 1902. 



