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-1903.] PHILLIPS—A REVIEW OF PARTHENOGENESIS. 301 
observed, showed true parthenogenesis, and Leuckart (1857) 
_ expressed the same opinion for Daphnia. In 1858 males of Asus 
were discovered and were examined by v. Siebold and he thus 
learned that some broods can go on developing parthenogenetically, 
like the Lepidoptera (Thelytoky), while other broods have both 
sexes present. For several years he watched a small pool near 
Munich, and at one time with great care removed every individual 
and found no males in 5796 individuals. In pools where both sexes 
occurred the proportion of males and females was very variable, and 
y. Siebold was led to believe that in these cases the males are dis- 
appearing, since from examinations in different years he found a 
constantly increasing proportion of females. 
v. Siebold foresaw the objection that males might have been 
present previous to the examination of the pools, and consequently 
‘examined the male genital organs and spermatozoa and then the 
ovaries and their development. He never succeeded in finding any 
spermatozoa in the female genital organs. The structure of the 
ovum made this observation decisive since he found a hard egg- 
_ shell formed in the uterus and no micropyle, so that if fertilization 
takes place it must be before the egg is laid. Brauer (1872) found 
that fertilized eggs of Afus produced males. 
Several other groups of Crustacea show a similar method of 
development, but do not differ toany extent from 4fus. Partheno- 
_ genesis has been observed in the Phyllopods, Ostracods and Cope- 
pods, but in none of the Malacostraca. 
In Artemia salina, Joly (1840) found no males in 3000 individ- 
uals examined and explained this as due to hermaphroditism, but 
Gerstacker (1867) and especially v. Siebold (1871) established this 
as a case of true parthenogenesis. In A. Milhauseniz, Fischer v. 
Waldheim (1834), Rathke (1836) and Fischer (in Midden- 
dorf’s Reise, Zoologie) found that males are rare, and the same is. 
true for Limnadia Hermanit, both cases being explained like that 
of A. salina. ‘The maturation of the parthenogenetic egg of 4. 
salina (Brauer, 1893) is discussed in another place. 
A case worthy of note is that of Zeptodora hyalina, a Daphnid, 
in which the winter eggs follow the usual plan of Crustacean devel- 
opment and form a Nauplius stage, while the summer eggs develop 
directly into an adult form with all limbs present. This is one of 
the striking cases which indicate that parthenogenesis is acquired 
ap v 
bi, a7) 
