42 T. H. MORGAN AND ELETH CATTELL 



body-color) be only 1 to 88. This difference is so small that it 

 affects the data given above only slightly. It could be accu- 

 rately estimated only by adding in to the two last calculations the 

 cross-over and coupled cases given in the 'small classes/ but this 

 addition involves the consideration of another matter, namely, 

 double-crossing-over. Without going further into the details of 

 this question the addition of the small classes would be mis- 

 leading. As the rhatter is especially considered by Mr. A. H. 

 Sturtevant in a paper appearing at the same time as this one, 

 the whole discussion may be left to his handling. 



