i54 
V. H. Blackman. 
A consideration of the cases of so-called parthenogenesis shows 
still further stages of reduction. A number of cases of thi 
process have been described amongst animals and plants but the 
majority of them, as Hartog 1 has pointed out, can lay no real claim 
to true parthenogenesis, which is the development of a potential 
gamete without relation to any other gamete. It is well-known, 
from the observations of Weismann and Ischikawa, Blochmann, 
Henking, etc*, that parthenogenesis occurs in Rotifers , in various 
groups of Crustacea ( Daphnidae , Polyphemidae, Artemia) and in 
various insects ( Aphides , Hymenoptera ), but in the majority of cases 
the cell from which the embryo develops is not a normal egg, but 
one which has not formed a second polar-cell and is really the 
mother-cell of two gametes 2 . It has not undergone a reducing 
divisions and thus has the nuclear characters of a somatic cell with 
the double number of chromosomes, and is incapable of fertilisation. 
Clearly the formation of actual gametes has in these cases been 
suppressed and the process of development partakes of the nature 
of somatic budding. 
A stage of development which connects most strikingly this 
process of somatic budding (“parthenogenesis”) with that of 
normal fertilisation is that described by Brauer for the eggs of 
Artemia salina. Though the majority of the “ parthenogenetic ” 
eggs of this animal form only one polar-cell, yet a second one is 
produced in a few cases. This, however, is never extruded from the 
egg, but its nucleus, after moving a short distance away, returns to 
the egg nucleus and behaving like the nucleus of a spermatozoon 
fuses with the latter and thus brings the chromosomes up to the 
normal somatic number again. 3 The normal process of fertilisation 
is thus replaced by an endogamous union of sister gametes. 
A certain number of cases of this form of “ parthenogenesis” have 
been observed in Angiosperms, and allowing for a difference due to 
the alternation of generation in the plants, the similarity with the 
process described above for animals is exact. The development of 
1 Quart. Jour. Microsc. Science XXXIV., (1901) p. 
2 It is now well established that the polar-cells represent merely 
three abortive eggs, and that they, with the egg, correspond 
with the tetrad of spermatozoa which are formed from one 
mother-cell; the first polar-cell represents two abortive eggs, 
the division, however, being usually, but not always, 
suppressed. 
3 The failure, later, of Petrunkewitsch (Anat. Anzeig. XXI., (1902) 
p. 250) to observe this process is probably to be explained as 
Castle (Bull. Mus. Comp. Zool. Harvard XL. (1903) p. 204) 
suggests, by the fact that the former investigated only winter 
eggs. 
