58 Mr. F. Merrifield on effects of temperature 
It will have been observed that no less than 8 out of 
31 of those P. napi which entered the pupal stage (7.e., 
more than a fourth) had made their election, if I may 
use the expression, to belong to the spring emergence. 
This spontaneous splitting of a brood into the two emer- 
gences 1s a common occurrence (attributable, as I 
believe, generally to individual congenital causes), with 
many double brooded species, and notably with P. napi. 
Professor Weismann records (‘ Studies in Heredity,’ by 
Meldola, pp. 39, 40) that a whole brood of his went over 
in this manner, and thinks this may have been owing 
to the mechanical motion to which they were subjected 
in a seven-hour railway journey, but I should question 
whether the occurrence was not rather to be ascribed to 
a congenital tendency happening in his case to affect all 
the individuals of the brood; in other species I have 
often known a whole brood go over in this way. His 
statement that the butterflies from eggs laid by the 
spring emergence of P. napi under ordinary circum- 
stances always emerge in the summer, generally in 
July, of the same year, is I think not in accordance 
with the experience of many English collectors. Mr. 
Hawes informs me that of a large brood he had, more 
than half went over to the spring. 
VY. atananta.—This is an insect which generally varies 
but slightly in appearance, and from which I should 
not have expected such results as have been in fact 
obtained. 
I collected more than 100 larve with a few pup between 24th 
August and 16th October last. About 15 per cent. died from 
having been attacked by parasites. 
My first temperature divisions were as follows :— 
(1) At between 80° and 90°; these all emerged in 6 days. 
(2) At the room temperature, 62° to 69°, averaging about 64° ; 
these emerged in 18 to 19 days. 
(3) In a cellar at an equable temperature of about 56°; emerging 
in about 34 days. 
(4) In a cool place out of doors, at about 51° to 64°, averaging 
54° oriess; these emerged in 44 days. 
(5) In the refrigerator, averaging about 45° by day, and in the 
room by night, averaging about 58°; 51° being about the general 
average, and the insects emerging in about 40 to 50 days. 
Classes 2, 8, and 4, ¢.¢., those at temperatures from about 54° to 
