No. 524] CHROMOSOMES AND HEREDITY 467 



angles to the plane of union, and that only at the second 

 division does separation or segregation occur. In fact 

 the assumption of separation is largely gratuitous, and 

 is the outcome of certain theoretical postulates of Weis- 

 mann's theories — postulates that rest in part on ques- 

 tionable evidence. 



All that we really know is that in some cases two longi- 

 tudinal divisions of the chromosomes occur. 2 whose rela- 

 tion to the plane of fusion is largely hypothetical. If, 

 however, it be assumed that the chromosomes simply 

 come to lie side by side (or even end to end) and later 

 separate the process of synapsis, as it is called, is 

 merely "touch and go" and has no deeper significance. 

 If, on the other hand, it be assumed that the synapsis is 

 a true fusion of the combining elements, there are no 

 reasons to suppose that the chromosomes separate later 

 into their constituent parts. The expectation is rather 

 that once completely fused they do not necessarily sepa- 

 rate at the plane of fusion to give the pure elements that 

 combined. 



It is, however, the assumption that the chromosomes 

 do separate along their line of union that has appeared 

 to some writers to have important hearing on the theory 

 of Mendelian theory of pure gametes. Let us therefore 

 assume for the moment that the separation takes place 

 in this way. Since the number of chromosomes is rela- 

 tively small and the characters of the individual are very 

 numerous, it follows on the theory that many characters 

 must be contained in the same chromosome. Conse- 

 quently many characters must Mendelize together. Do 

 the facts conform to this requisite of the hypotheses! 

 It seems to me that they do not. A few characters, it is 

 true, seem to go together, but their number is small, and 



