96 SEX INHERITANCE 



animal becomes and remains functionally male. 

 According to Baltzer, if the free swimming embryos 

 of the gephyrean worm, Bonellia, are isolated they 

 become sexual females. If however a swimming 

 embryo that is ready to settle down comes to 

 rest on the proboscis of a female, it develops into a 

 rudimentary but functional male. A few^ embryos 

 in each culture that do not settle down show signs 

 of becoming hermaphroditic. It has been sug- 

 gested (Geoffrey Smith) that the parasitic males 

 (** complementary males") of certain species of 

 barnacles owe their condition to their surroundings, 

 as in Bonellia. 



The most important information relating to the 

 chromosomes in hermaphrodites and unisexual forms 

 is that discovered by Boveri and Schleip from the 

 thread w^orm, Rhabdonema nigrovenosum. This 

 species has two generations in its life cycle. One 

 generation consists of parasitic hermaphrodites that 

 live in the lungs of the frog, the other consists of 

 free-living males and females. The hermaphrodites 

 and the free-living females have 12 chromosomes. 

 The males have 11 chromosomes. In the her- 

 maphrodite, both eggs and sperm are produced in 

 the same germ-tube. The egg after maturation 

 has 6 chromosomes. In the hermaphrodite two 

 classes of sperm are formed which, according to 

 Schleip, have 6 and 5 chromosomes respectively 

 (one X-chromosome having been lost at one di- 

 vision). The former fertilizing the egg produces a 

 free-living female, the latter a male. In the free- 



