SEX AND GENES 



215 



the same sporophyte mother cell produce female game- 

 tophytes and the other two male gametophytes. 



Somewhat later Allen discovered in the nearly related 

 group of liverworts (Fig. 124) that in the haploid female 



Y' 



Fig. 124. 



a, Female and b, male prothallia of liverwort. The female with 

 one large X-chromosome, a'; the male with one small Y-chromo- 

 some, b'. (After Allen.) 



prothallium (gametophyte), with eight chromosomes, 

 there is one (X) that is much larger than the other seven 

 chromosomes ; and in the haploid male prothallium (game- 

 tophyte), with eight chromosomes, one (Y) is much 

 smaller than the other seven (Fig. 121b'). Each egg will 



