308 PHILLIPS—A REVIEW OF PARTHENOGENESIS.  /[Oct. 16, 
not without reason be said: Parthenogenesis is the result of fer- 
tilization by the second polar body.’’ 
This conclusion was in part confirmed by Brauer (1893) on the 
parthenogenetic egg of Artemia salina. ‘There are two types of 
maturation in parthenogenetic eggs occurring in the same animal, 
one in accordance with the idea of Boveri and the other not irre- 
concilable with it. Fora brief description of the two methods in 
Artemia the statement of Wilson ' is quoted : 
Jn both modes typical tetrads are formed in the germ-nucleus 
to the number of eighty-four. In the first and more frequent case 
but one polar body is formed, which removes eighty-four dyads, . 
leaving eighty-four in the egg. There may be an abortive attempt 
to form a second polar spindle but no division results, and the 
eighty-four dyads give rise to a reticular cleavage-nucleus. From 
this arise eight-four thread-like chromosomes and ¢he same number 
appears in later cleavage stages. 
S Se 
“Tt is the second and rare mode that realizes Boveri’s concep- 
tion. Both polar bodies are formed, the first removing eighty-four _ 
dyads and leaving the same number in the egg. In the formation 
of the second, the eighty-four dyads are halved to form two daugh- 
ter groups, each containing eighty-four single chromosomes. oth 
these groups remain in the egg and each gives rise to a single reticu- 
lar nucleus, as described by Boveri in Ascaris. These two nuclei 
place themselves side by side in the cleavage figure, and give rise each 
to eighty-four chromosomes, precisely like two germ-nuclet in ordinary 
fertilization. The one hundred and sixty-eight chromosomes split 
lengthwise and are distributed in the usual manner, aud reappear 
in the same number in later stages. In other words, the second 
polar body here plays the part of a sperm-nucleus precisely as 
maintained by Boveri. 
‘*Tn all individuals arising from eggs of the first type, there- 
fore, the somatic number of chromosomes is eighty-four; in all 
those arising from eggs of the second type, it is one hundred and 
sixty-eight. This difference is clearly due to the fact that in the 
latter case the chromosomes are single and univalent, while in the 
former they are bivalent (actually arising from dyads or double 
chromosomes). ‘The remarkable feature, on which too much em- 
phasis cannot be laid, is that the numerical difference should 
1 Wilson, Zhe Cell in Development and Inheritance, pp. 281-284. 
