THE FUNDAMENTALS OF MENDELISM 



45 



zygotene, the point to point correspondence which it shows is probably 

 a special case of a general phenomenon. 



Less direct evidence that pairing is only between homologues is the 







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8 fn,p a.M/, 



v««, 





B 



,t 



i 1 



r- •■ f 



<> » -* 



«■■ 



'0 



Fig. 11. Zygotene Pairing. — A in a lily, the chromosomes showing a structure 

 of numerous small chromomeres ("ultimate chromomeres" (from Metz, after 

 Belling). 6 Three drawings of one pair of chromosomes from a grasshopper, 

 showing constancy of structure and homology of pairing elements; the chromo- 

 somes are shown at a lower magnification than k, and have a structure of larger 

 and less numerous chromomeres. (From Metz, after Wenrich.) C a pair of chromo- 

 somes in Trillium (from Huskins and Smith). D. Fritillaria Eggeri, notice that the 

 contraction and condensation of the chromosome has progressed farther near the 

 centromeres, which are very closely paired at a. (From Darlington.) 



fact that pairing normally fails completely in haploids (but see p. 72), 

 while in triploids pairing is in threes, in tetraploids in fours, and so on 

 (p. 68). Evidence of a similar kind was obtained by Gelei;^ in Dendro- 

 coelum the premeiotic division was sometimes irregular, leaving one of 

 the daughter nuclei in two parts, and in some cases the smaller part 

 1 Gelei 1913, 1921, 1922. 



