si-:.\ 



365 



the Y in place of i !,<• X and develop into male gametophytes. The same 

 condition has been reported for Sphoerocarpos tezanus (Miss Schacke 

 1919). 



Although the situation in Sphoerocarpos suggests the XY type of sex 

 inheritance in Drosophila and other forms, it differs in several respects, 



iiiiiii 



Male gametophyte 



IIIIIII' 



Female gametophyte 



Fertilized 

 egg 



Sporophyte Sporocyte 



Maturation divisions 

 SPHAE.K0CARPU5 



IIIIIII 



Male gametophyte 



I I Hill' 



Female gametophyte 



6 &> 



Fig. 142. — The history of the chromosomes in the life cycle of Sphoerocarpos. I 



data of C. K. Allen, 1917, 1919.) 



as Allen (1919) points out. In Sphoerocarpos the separation of the XY 



pair results in the production of two kinds of spores which develop directly 



into haploid organisms (gametophytes) of two sexes, whereas in Droso- 



phila the corresponding separation results in two sorts of male gametes 



which determine the sexes of the 



diploid organisms developing from 



the eggs they fertilize. Furthermore, 



in animals wit h sex-chromosomes some 



forms show the presence of XX to be 



correlated with femaleness and X or 



XFwith maleness (male heterozygous 



for sex), while in other forms XX ™** :l " d [TnL^m^An^r E 

 •'» _ Sphavrocarpos Doumlhi. ifter < . /. 



is correlated with maleness and X AUen, 1919.) 



or XY with femaleness (female 



heterozygous for sex 1 )- There is evidence to show thai the K-chromo- 



some carries no sex-factors in these cases, 2 though its absence may result 



in sterility (Bridges). (See Chapter XVII.) In Sphoerocarpos, on the 



1 Sex-chromosomes referred to in this case as Z and W rather than X and Y, 



2 £oe in this connection Castle 1921. 



Fig. l 13. ( Jhromosome groups from 



