314 PHILLIPS—A REVIEW OF PARTHENOGENESIS,  [Oct. 16, 
ber may be retained in parthenogenetic eggs the reduction division 
is omitted, or in some other way the same result is accomplished. 
This omission of a mixing of two lines of ancestry in the repro- 
duction of a species is, if our conception of its significance is 
correct, a very important one. There is, however, a great differ- 
ence in the extent of this omission in the various kinds of partheno- 
genesis. In Arrenotoky at every second generation a crossing 
occurs of necessity, since the females are produced from fertilized 
eggs. In Thelytoky, on the other hand, a mixing may be very rare 
or even entirely wanting; while in Amphoterotoky it generally 
occurs at regular intervals, as in the fall in Aphids. On the other 
hand, Thelytoky and Amphoterotoky are much more beneficial to a 
species from the standpoint of its propagation, since at no time is 
fertilization an absolute necessity, while in Arrenotoky fertilization 
is necessary for the production of the individuals which do the 
most toward the reproduction of the species. What the species 
loses in hereditary influences is more than made up by the increased 
advantage of these two most specialized kinds of parthenogenesis. 
Pedogenesis—lf we look on parthenogenesis as a phenomenon 
which has arisen in various groups of animals so that the species 
may be reproduced rapidly and without so much dependence on 
chance, then it is but another step in the same direction to find this 
process shifted back to an embryonic stage of development so that 
the reproduction would not be delayed until the female reached the 
adult state. The same precocious segregation of the reproductive 
process is met with in forms which always require the fertilization 
of the egg, ¢.g., Amdlystoma (Axolotl), but in these cases the coin- 
cident phenomenon of parthenogentic development has not been 
necessary or desirable and we distinguish such cases as Proiogony. 
We may look on certain groups of the Diptera as in a transition 
stage, between the parthenogenesis like that observed in Chivonomus 
Grimmit and that of Mastor. The species of Afzastor has still 
further acquired the advantage of viviparity for the protection of the 
youngest embryonic stages, and seems almost to have reached the 
limit of advantage that a species can acquire for the propagation of 
its kind. 
Partial Parthenogenesis.—As has been seen, eggs which have not 
been fertilized often begin to develop, but after a short time die. 
On this account it has been argued that such cases are not really par- 
thenogenesis, since an adult or a sexually mature individual does not 
