L. ARGIOLUS MONOGONEUTIC AND DIGONEUTIC. 51 
under consideration; it is here no question of climate, but 
apparently simply of food; the problem has for a long time 
occupied my thoughts, and I venture to offer an explanation. An 
insect feeding either on the bloom, buds, or tender shoots of the 
holly only must be single-brooded, as that tree makes its growth 
in the early months of the year; and the hard leaves, which alone 
would be on the tree at the period of the summer emergence in 
July and August, would probably be not succulent enough for the 
small larve then produced from the ova. 
The ivy, on the other hand, makes shoots not only in the 
spring, but during the whole of summer; and even as late as 
October growth has not ceased, as I have found to be the case 
with some forty varieties of ivy I have cultivated for more than 
thirty years. 
I believe that the holly and ivy are considered to belong 
to the remains of the old miocene flora, and it is probable that 
the ancestors of LZ. argiolus may have fed on the trees from which 
these two species have been respectively phylogenetically derived. 
However this may be, I think it may be taken for granted that at 
one time Li. argiolus was single-brooded, and that the summer 
brood has been acquired, as in the case of Pieris napi before- 
mentioned. 
Now, what would occur if Pieris napi was deprived of all food 
for the larvee produced from the ova of the second emergence of the 
imago? Many would say the species would cease to exist. I say 
no, it would not, for this reason: all who have had to do with 
double-brooded insects know perfectly well that many of the pupze 
of the summer brood do not produce their imagines, say, in July 
or August, but, on the contrary, they remain in the pupa-state 
till the proper period of emergence in the next spring arrives. 
This is certainly true of P. napi, and the fact is adverted to by 
Weisman. 
In this very genus Lycena I have thought that L. bellargus, 
although double-brooded, is very much rarer on the wing in 
July and August than in June, and that probably many pass the 
winter in the pupal as well as in the larval state. I do not feel 
quite certain that the same race of L. argiolus feeds both on 
the holly and ivy; it is more probable that we have two 
races—one monogoneutic, confined to the holly, and the other 
digoneutic, feeding on the ivy. Both the late Mr. Buckler and 
