VIABIUTY OF GAMBUSIA 
199 
of females had died, hut no males. This mortality had doubtless 
been caused by the rapidly increasing temperature of the water 
in which the fish were shipped. It is evident, then, that the male 
Gambusia is somewhat more resistant to higher temperatures than 
the female. That the significance of temperature in this matter 
is nil is suggested by the fact that the writers have seen on sev- 
eral occasions Gambusia thriving with no mortality in pools where 
the water registered from 97 to 103 degrees Fahrenheit. (Italics 
mine.) 
It seems to me that the fact that no males were found by Barney 
and Anson in the death population, while many females were, has 
little or no significance, for there is nothing in the passage cited, 
or elsewhere in the paper, to show that the sex-ratio of the popula- 
tion as shipped had been ascertained. It will be seen from the 
table that in my shipments from 68.3 per cent to 75.9 per cent of 
the fish that were dead on arrival were females. In view of the 
fact that the sex-ratios were 256.8 and 774.7 females, respectively, 
to every 100 males it will be seen that this is owing to the fact 
that the males were so greatly outnumbered by the females. Is 
it not possible, then, that the low death-rate in the males claimed 
by Barney and Anson may have been due to a deficiency in the 
number of males present? If this was true, it might be ac- 
counted for by the operation of either or both of two causes: (a) 
at this season of the year, the percentage of males in a population, 
is about at its low-point,^ or, (b) the males, being much more 
agile, and of markedly smaller size than the females, often either 
avoid or pass through the net, during the collecting. Barney and 
Anson do not say what kind of net was used in making the collec- 
tion, but in the course of their paper (p. 55) they state that all 
collections summarized in their tables were made with quarter- 
inch meshed seines and dipnets. Judging from the results of my 
own experiments, I am sure that with such a net, many Gambusia 
pass through the meshes, and that most of these are males. It 
may be, then, that in the collection made by Barney and Anson, 
a large proportion of the males escaped, and if this is true, it is 
a simple matter to account for the lack of males in the dead popu- 
lation referred to. 
On the basis, merely, of the sex-ratios and mortality rates of 
these two collections sent to me from Beaufort, I should be quite 
unwilling to draw general conclusions as to the differential via- 
bility of the sexes in Gambusia. Mr. S. F. Hildebrand, however, 
2 1 am assuming that Barney and Anson are correct in their conclusions on this 
point; I have no data of my own. 
