4 
; 
es 
Br 
1903.] PHILLIPS—A REVIEW OF PARTHENOGENESIS. 813 
males and females remained approximately the same under all food 
conditions, and concluded that sex is determined in the ovary in 
insects. 
There have recently appeared two papers of interest in this con- 
nection as offering suggestions for future work. Beard (1902) and 
v. Lenhossek (1903) conclude, on theoretical grounds, that sex is 
determined in the ovary of the mother and that there are in all 
cases two kinds of eggs, male and female, fundamentally differing 
from one another. Cases where such a state of affairs is known 
to exist are Phylloxera, Dinophilus, some Rotifers and _pos- 
sibly in Raza batts (Beard, 1902). According to these views, the 
sex is determined before leaving the ovary and consequently fertil- 
ization can have no influence, but at present we cannot look on 
these theories as more than interesting suggestions. It must be 
admitted that the determination of sex by fertilization is in direct 
opposition to what we know to be true for the great majority of 
animals where both sexes alike arise from fertilized eggs, and on a@ 
priort grounds the theory of Cuénot, Beard and von Lenhossek 
seems probable; but in this instance, as in all others in zoology, @ 
priori reasoning is unsafe and we must wait for future investigations 
to decide whether there is any truth in these suggestions. 
Comparison of Various Sex Relations.—As has been pointed out 
by several investigators, the process of fertilization has two distinct 
purposes—the giving of a stimulus for development to the mature 
egg, and the increasing of the number of hereditary tendencies of 
the offspring by giving it a blending of hereditary traits from two 
parents. The power of parthenogenetic development possessed by 
some animals takes the place of the stimulation of the male sex cell, 
since the ovum has given to it in the ovary enough vital force to go 
on dividing mitotically even after it becomes a part of another gen- 
eration. 
The second office of fertilization is simply omitted where fertil- 
ization does not occur, the advantage of agamic development more 
than balancing the advantage to be gained by the meeting of two 
lines of heredity. During ordinary maturation the egg gives off in 
its polar bodies one-half of the number of its chromosomes, the 
heredity carriers, and by the aequisition of an equal number from 
the male cell, carrying hereditary tendencies from the male parent, 
the original number is regained ; and in order that the normal num- 
PROC, AMER. PHILOS. SOC. xLiI. 174. V. PRINTED DEC. 15, 1903. 
