(ae) 
tion between the two latter crosses. The offspring of the 
first crosses were roughly divisible into two groups following 
the parent forms, those of the second tended to become 
quite different in appearance. Hybridization led to the pro- 
duction of continuous broods, and certain broods tended to 
produce males only. The coloration became more intense 
with increase in the duration of the pupal stage. 
Dr. Dixry drew attention to the experiments on hybridiza- 
tion recorded in Dr. Standfuss’s ‘‘ Handbuch der Paliarktischen 
Gross-Schmetterlinge.’’ These had been continued for many 
years, and accounts of them had appeared from time to time 
in various foreign periodicals. They were now published at 
length, and it would be recollected that several of the hybrids 
themselves, together with interesting specimens of tempe- 
rature-variation, had, through the kindness of Mr. Merrifield, 
been exhibited during the past summer in London. Some 
of the chief conclusions derived by Standfuss from his nume- 
rous experiments in the crossing of macrolepidoptera were 
briefly summarized as follows :— 
A. The fertility of first crosses. 
1. The intercrossing of two species may result in anything 
from complete sterility to the production of the normal 
number of fertile eggs. These extremes may even occur as 
the result of crossing different individuals of the same two 
species. 
(Hence a cross must not be pronounced infertile on the 
evidence of a single failure.) 
2. Individual differences in the structure of the genital 
apparatus may prevent effective crossing between some 
members of two given species, though other members of 
the same two species may pair freely. 
3. Some crossings have resulted entirely in male, others 
entirely in female offspring. A third class has given both 
sexes in various proportions. 
B. The fertility of hybrids, 
4, In no case observed by Standfuss or known to him has 
the female of a true hybrid been shown to be fertile. But the 
