94 



EDMUND B. WILSON 



the other types (C-G), 8 or the more complicated ones shown in 

 fig. 5. I represents the possible mode of separation of the 

 X-element from a YY-pair, as suggested by Stevens; and this 

 may be realized in Ascaris megalocephala (H). J and K are 

 schemes of the relations seen in Hesperotettix, Anabrus and 

 Mermiria (cf. fig. 6). These may be direct derivatives of a 

 primitive XY-pair, as the diagram suggests, or may be a result 



C. Thyanta 

 X 



XY-Pair 



I 



Idiochromosome 

 Pair 



Y 



,1 I 



T.? I 



D. Fitchia 



.. Conorhinus 

 X 



G. Syrornastes 



Mermiria, 



/i.Ascaris 



' Jfesjberofattix 



Fig. 7 Diagram illustrating the possible relation of the various types of idio- 

 chromosomes to a primitive XY-pair. Explanation in text. 



of secondary coupling of X with other elements. In either case 

 X may itself have such a composition as is indicated in F (Prote- 

 nor). 



(c) Sex-limited heredity. (1) The foregoing considerations have 

 an important bearing on the problem of sex-limited heredity, 

 for they give us a very definite view of how such heredity may be 

 effected. It is not my intention to consider this subject in ex- 



8 These figures are not intended to indicate the precise mode of segregation of 

 the X- and Y-chromatins of the X-element, but only illustrate possible modes. 



