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 worm, 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- 
