194 GERM-CELL CYCLE IN ANIMALS 
divide before the sperm nucleus fuses with it, the 
latter may unite with one of the daughter nuclei 
of the egg nucleus; this cell with this double nucleus 
might then produce female structures, whereas the 
other cell with only a single nucleus representing one- 
half of the egg nucleus might give rise to male char- 
acters. Morgan has proposed another theory which 
is based on the fact that more than one spermatozoén 
is known to penetrate the eggs of insects. If one 
of these supernumerary spermatozoa should chance 
to divide, it might result in the formation of male 
structures, whereas the cells containing descendants 
of the egg nucleus fused with another sperm nucleus 
would exhibit female characteristics. 
There is some evidence that true hermaphroditism 
may exist among insects, at least during their embry- 
onic and larval stages. Thus Heymons (1890) has 
described in a young larva of the cockroach, Phyllo- 
dromia germanica, what appear to be rudimentary 
egg-tubes, and in another larva eggs were found in 
the testes which resembled those present in the egg- 
tubes of female larve of the same size (1 mm. in 
length). More recently, Schénemund (1912) has 
reported the presence of egg-tubes attached to the 
anterior end of the testes of stone-fly nymphs (Perla 
marginata). 
True hermaphroditism is rare in man and other 
mammals, but several cases have been described in 
the pig by Sauerbeck (1909) and Pick (1914), and in 
man by Simon (1903), Uffreduzzi (1910), Gudernatsch 
(1911), and Pick (1914). 
