622 NATHAN FASTEN 



quartered in number by two successive reduction divisions. This view 

 was founded especially by O. Hertwig ('90) and Wilcox ('95). 



B. The univalent chromosomes undergo neither conjugation nor 

 pseudoreduction during the prophases, but conjugate first in the equator 

 of the first maturation spindle and there separate reductionally. Found- 

 ed by Henking ('91) and Korschelt ('95). 



C. The univalent chromosomes undergo pseudoreduction in the 

 prophases by a continuous chromatin spirem segmenting into half the 

 normal number of segments ; these divide equationally in the first mitosis 

 and reductionally in the second; Riickert ('93, '94) Hacker ('95), Vom 

 Rath ('95). 



D. There is no continuous chromatin spirem produced in the pro- 

 phases, but the univalent chromosomes conjugate to form pairs or 

 gemini and these undergo a reductional and an equational division. 

 This view, now shared by the great majority of students exhibits itself 

 under these aspects: 



D. 1. The chromosomes conjugate metasyndetically. 



(a) The reduction in the number of the chromosomes is effected by 

 the first naturation mitosis (Montgomery, '00; Farmer and Moore, 

 '03). 



(b) The reduction in the number of chromosomes is effected by the 

 second maturation mitosis (McClung, '00, and his students). 



D. 2. The chromosomes conjugate parasyndetically and the first 

 maturation mitosis is reductional. Winniwarter ('00), Gregoire ('04), 

 Berghs ('04), A. and K. E. Schreiner ('04, '05). 



My own studies, as set forth in the present paper, are in har- 

 mony with the last of these views, i.e., D 2. No continuous 

 spireme is formed, the chromosomes unite, side by side, into 

 gemini, and reduction occurs in the first maturation division. 



Within the last few years the view that chromosomal con- 

 jugation is parasynaptic has been strongly advocated by many 

 investigators. Von Winniwarter ('00), first called attention to 

 this type of union in the mammals. But in that period the view 

 mainly gained ground among botanical cytologists, and w^s 

 strongly advocated by them. The botanists called attention to 

 the stages preceding synapsis, the 'presynaptic stages' in the 

 growth period and showed that these are the most important for 

 a concise study of conjugation. 



The Schreiners ('04, '05, '06, '07 and '08), more than any- 

 body else, have worked on this phase of synapsis in animals, 

 and have shown parasynapsis to occur in the following forms: 



