56 STUDIES IN SPERMATOGENESIS. 



character, having become dominant in certain eggs at an early stage, 

 may, from that time on, determine the kind of development. As to 

 the second alternative, I see no reason for supposing that the small 

 heterochromosome of a pair is in any different condition, as to activity, 

 from the large one. The condensed condition may not mean inactiv- 

 ity, but some special form of activity. And, moreover, it has been 

 shown that in certain stages of the development of the oocyte of one 

 form, Aphrophora quadrangularis , there are pairs of condensed chro- 

 mosomes corresponding to those of the spermatocyte, so that there 

 would hardly seem to be any basis for Wilson's attempt to associate 

 the difference in development of male and female germ cells with 

 activity or inactivity of chromosomes, as indicated by condensed or 

 diffuse condition of the chromatin. 



On the whole, the first theory, which brings the sex determination 

 question under Mendel's Law in a modified form, seems mostin accord- 

 ance with the facts, and makes one hopeful that in the near future it 

 may be possible to formulate a general theory of sex determination. 



This work has been done in connection with a study of the problem 

 of sex determination, but, whatever may be the final decision on that 

 question, it brings together a mass of evidence in favor of the belief in 

 both morphological and physiological individuality of the chromo- 

 somes, as advocated by Boveri, Sutton, and Montgomery. It also 

 gives the strongest kind of evidence that maternal and paternal homo- 

 logues unite in synapsis and separate in maturation, leaving the ripe 

 germ cells pure with regard to each pair of characters. 



Bryn Mawr College, June 7, ipo6. 



