296 PHILLIPS—A REVIEW OF PARTHENOGENESIS.  [Oct. 16, 
v. Siebold (1839) examined the viviparous and oviparous females 
and found that there is no appreciable difference between the 
ovaria of the two, but that the former lack a receptaculum seminis, 
and are, therefore, incapable of copulation. In the former point 
he was confirmed by Owen (1849), but: not by Steenstrup (1842), 
who insisted that the viviparous individuals do not have ovaries 
but a. well-developed uterus ; to these he gave the name ‘‘ Ammen ”’ 
or nurses. 
A most important step in advance was made by Steenstrup 
(1842) when he introduced the idea of an Alternation of Genera- 
tions in Aphid development, as well as for other forms. He and 
Carus (1849) concluded that the viviparous development is com- 
parable to the Cercaria stage of the Fluke worm, and the theory, 
first suggested by Duvau (1825), that here we have two generations, 
each distinct from the other, but each in turn giving rise to the 
other, was strengthened. Steenstrup would not, however, admit 
that the viviparous development is at all comparable to the ovipar- 
ous, for he wrote: ‘‘No true ovary has been discovered in the 
larval and larviparous Aphids, but the germs, as soon as they are 
perceptible, are situated in organs which must be regarded as 
291 
oviducts and uteri. 
About this time the theory of Dzierzon (1845) was advanced for 
the parthenogenetic development of the drone eggs of the Honey 
Bee, but such an explanation was not accepted for Aphids, and even 
v. Siebold, in his celebrated paper, ‘‘ Wahre Parthenogenesis bei 
Schmetterlingen und Bienen’’ (1856), although advocating par- 
thenogenesis for the forms on which he worked, refused to admit 
it for plant lice, for he wrote: ‘‘ Die viviparen Blattlause keine 
Weibchen sind, welche sine concubitu im jungfraulichen Zustande 
entwicklungsfahige Ejier hervorbringen, sondern geschlechtlose 
mit Keimstécken ausgestattete Ammen-oder larvenartige Individuen, 
welche von den wirklich jungfraulichen Blattlause-Weibchen him- 
melivert vorschieden sind.’’ ? 
Owen (1849) applied the term Parthenogenesis to the develop- 
ment of Aphids, not in the sense in which it is now used, but as an 
equivalent of the term Alternation of Generations used by Steen- 
strup. Owen thought that the fertilization which takes place in 
1 Page 112, English translation. 
2 Page 14, loc, cit. 
a“ 
