4 
— 
oe 
a? 
1903.] PHILLIPS—A REVIEW OF PARTHENOGENESIS. 299 
eggs or, because of the fact that they remain undeveloped for some 
time after fertilization, Dawereter or retarded eggs. 
DipTERA.—This group furnishes some excellent examples of 
pzedogenesis or pedoparthenogenesis, and the phenomena as shown 
in various genera grade into each other in such a manner that it 
becomes evident that no line of demarcation can be drawn between 
parthenogenetic development from eggs laid by adult females and 
pedogenesis. While it is perhaps well to make a distinction 
between the phenomenon of parthenogenesis as exhibited by eggs of 
adult females and the same phenomenon as shown by the eggs of 
females which have not yet reached the last or adult stage of their 
development, yet the fundamental principle is the same in each 
case and it is not well to put too much stress on the degree of 
development of the parent when such a distinction tends to hide 
the similarity of the two kinds of reproduction. 
Wagner (1862), in a Russian paper, reported cases of fly Jarve 
which bring forth young viviparously and, as he thought, from a 
transformation of the fat body, the parent dying at the birth of the 
offspring. This was in opposition to every principle of zoology 
and was, of course, not accepted on account of the announced 
method of formation of the embryos. In a short time, however, 
v. Baer (1863) and Meinert (1864) confirmed Wagner in all points 
except the source of the young, and later Wagner came to the con- 
clusion that the viviparous young, are developed from true eggs. 
These conclusions were confirmed by Ganin (1865). The forms 
worked on were Mastor and Cecidomyia. 
The next phenomenon of the series is that shown in Chironomus 
(Grimm, 1870). Here the use lay eggs which develop partheno- 
genetically. This case comes nearer to what is observed in 
Hymenoptera, and the next step, which completes the series, is that 
of Chironomus Grimmit (Schneider, 1885) in which the imago 
lays parthenogenetic eggs. 
Without going into a discussion of other forms on which work 
has been done, it will be evident that here we have a series of cases 
in which the Cecidomyidz have reached the most specialized con- 
dition, they being able to bring forth young viviparously from a 
larval parent without waiting for the parent to reach the adult con- 
dition before acquiring sexual maturity. The case reported by 
Grimm for Chironomus would then appear to be one in which this 
power of bringing forth young very soon had not been so com- 
