212 



GENETICS 



ondary sexual characters, and also that the determin- 

 ers for the opposite sex are often present in a latent 

 condition, or, in other words, that the organism, 

 either male or female, is heterozygous with respect to 

 sex. 



If a female of the annelid worm Ophiotrocha, for 

 example, is cut in half, it is effectually castrated, be- 



Male 



Parasitical^ castrated male 



Female 



FIG. 64. The crab, Inachus, parasitized by the cirripede, Sacculina. 

 Evidence that a Mendelian sex determiner is correlated with " sec- 

 ondary sexual characters " and that the male is heterozygous for sex 

 while the female is homozygous. After Smith. 



cause the ovaries are in the posterior part of the body. 

 It has the power of regeneration, however, but when 

 a new posterior part is formed, it contains, not female, 

 but male reproductive organs. The worm is, there- 

 fore, now a male, as shown by the presence of testes 

 instead of ovaries, proving that it was originally 

 heterozygous with respect to sex. carrying one sex 

 latent. 



