Twenty seventh meeting. 



Schermcrlwrn Hall, Columbia University. February ig, 1908. 

 Vice-President Morgan in the chair. 



29 (285) 



An exhibition of photographs of chromosomes, with explana- 

 tory comment. 



By EDMUND B. WILSON. 



\From the Laboratory of Zoology, Columbia University .~\ 



The speaker exhibited a series of lantern-slides from direct 

 photographs, showing the sexual differences of the chromosomes 

 in a number of species of insects. The facts have now been 

 determined in nearly sixty species, all of which conform to the 

 same principle that the spermatozoa are of two numerically equal 

 classes, one of which is male-producing, the other female-produc- 

 ing. This is proved by the relations of the chromosomes. The 

 two classes of spermatozoa show certain constant differences in 

 this regard, differing in respect to one pair of chromosomes, and 

 in a few cases in respect to two or three pairs. The somatic 

 chromosome-groups of the two sexes show precisely parallel dif- 

 ferences in every known case ; and a study of the facts in detail 

 proves that these differences must be due to the fertilization of the 

 egg by one or the other class of spermatozoon. This conclusion, 

 first reached by strictly cytological researches on the germ-cells 

 of insects, has recently received complete experimental confirma- 

 tion in the work of Correns on the diecious flowering plants. 



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