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 



X.... 



saSU 



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 



