THE 



AMERICAN NATURALIST 



Vol. LIV. May- June, 1920 No. 632 



CHIASMATYPE AND CBOSSING OVEK 



PROFESSORS E. B. WILSON and T. H. MORGAN 



Columbia University 



Two short papers by Janssens, published in the 

 Comptes Rendus of the Societe de Biologie for April and 

 May, 1919, outline an interpretation of the maturation- 

 phenomena in Orthoptera in agreement with his earlier 

 chiasmatype-theory ('09) based on the corresponding 

 phenomena observed in urodeles. It is a matter of so 

 much importance that all phases of this question be fully 

 discussed that we venture to report and examine the con- 

 clusions announced in these new communications. For 

 this purpose we have found it convenient to divide the 

 discussion into two parts, one dealing with the matter 

 more from the standpoint of strictly cytological observa- 

 vation, the other more from that of the possibilities sug- 

 gested by genetic analysis. In order to avoid repetition 

 we have numbered the figures consecutively, but each 

 author is responsible for the part under his name. 



I 



A Cytological View of the Chiasmatype Theory 

 E. B. WILSON 



Professor Janssens 's results are as yet illustrated only 

 by diagrams, w T hich leave us in doubt concerning some 

 very important details ; nevertheless, a cytologist may be 

 permitted to indicate at this time how the conclusions 

 are related to those of other cytologists who have ex- 

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