ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
307 
mentions 0*1 mm. as tlie minimum diameter for an ovum wliicli will 
develop into a female, Nussbaum reared a living female from an ovum 
0*08 mm. in diameter. 
Maupas observed that the development of the parthenogenetic (“ sum- 
mer ”) eggs takes 26 hours at 15° C. and 12 hours at 24° C. ; Nussbaum 
notes that the rate of development is also influenced by the oxygenation 
of the water, by the behaviour of the Euglende which form the normal 
food-supply, and so on. 
Maupas also states that a parthenogenetic female will produce per 
diem at 15° C., 18 eggs, which become males, or 7 which become females, 
but at 21° C., 27 or 18 respectively ; Nussbaum notes that these figures 
are maxima, and are much reduced when a large number of individuals 
are living together. The length of life of the parthenogenetic female 
was estimated by Maupas as 13 days at 18° C. Four days before death 
the female laid its fiftieth and last egg. An effectively fertilised female 
lived 7-8 days at 18°-20° C. 
Nussbaum found spermatozoa inside the hard shelled ova; there is 
no doubt that they are fertilised. It remains, however, an open ques- 
tion whether Maupas is right in believing that only those eggs destined 
to become males are capable of fertilisation, and that when this happens 
they become hard-shelled eggs. 
As has been noted, a given ovary produced only males, or only 
females, and Maupas concluded that the sex of the grandchildren is 
determined in the ovary of the grandmother. Lowering the temperature 
determines that the ova will develop into females, and conversely ; but, 
after this early determination has been established, no environmental 
changes can affect it. He supported this by various experiments, which 
Nussbaum criticises. Maupas isolated five females, before maturity, 
and kept them at 26°-28° C. They produced 104 ova, which gave rise to 
females, of which 97per cent, had male eggs, and 3 per cent, female eggs. 
Five females of the same age and from the same culture, at 14°-I5° C., 
produced 260 ova, which gave rise to females, of which 5 per cent, had 
“male eggs,” and 95 per cent, “female eggs.” Maupas does not state 
whether he estimated the sex from the size of the eggs or from the 
.^actually hatched offspring. Nussbaum, by an analysis of the experiments, 
seeks to show that there were other differences in the conditions besides 
those of temperature. The nutritive conditions and the number of 
associated individuals have also to be considered. 
Prof. Nussbaum goes on to give an account of his own numerous 
experiments. We must make a selection from among the results, which 
are unfortunately not arranged methodically. One and the same female 
always produces a uniform brood. A male lives from two to three days. 
Temperature does not influence the sex of the brood produced by a sexu- 
ally mature female ; but cold retards development and productivity. 
With lowered temperature “ winter eggs ” tend to be produced. It is 
not possible to predict the sex of the embryo from the size of the egg. 
Females inseminated early and well fed during their growth produce 
only female summer eggs ; females inseminated early and ill fed produce 
winter eggs, from which, so far as is known, only females arise. If a 
parthenogenetic female is well fed from its emergence till it lays its 
first egg, only female eggs are laid ; if ill fed only male eggs. But the 
