ON EMERGENCE OF THE GRYPOCERA AND RHOPALOCERA. 109 
Europe as far as England, which emerge contemporaneously with 
those of the bigenerates: the first from April to June (according to the 
locality and the years, which are more variable than in the south), and 
the second, often very partial, from the end of July to the beginning 
of September. Brassicae generally follows this rule, but in very 
favourable years produces a third brood, which is abundant when the 
second brood has emerged precociously from the end of June to the 
beginning of July. Sporadic individuals of various species are fre- 
quently seen in October, but it is the case of precocious autumnal 
individuals of the first brood, which do not constitute in the British 
Isles a third brood, as in analogous cases they do not constitute a fourth 
brood in Italy. 
Brassicae offers, on the contrary, in England a good example of 
the true transformation of a trigenerate into a bigenerate, which 
gradually shows itself in more or less favourable years. This recalls 
the analogous phenomenon produced by altitude observed in the Alps, 
and contrasts with the phenomenon of simple ‘‘ suppression ’’ of one 
brood, without changing the epoch of the others, which happens in some 
localities and years in peninsular Italy. To suppression is generally 
to be attributed the missing emergence of the second brood of machaon 
in England. It is already constantly reduced to two broods, but in the 
colder summers the second brood is missing altogether; in those less 
cold a greater or lesser number of individuals complete a summer 
cycle, and their progeny succeeds in becoming chrysalids in time to 
winter with the remainder of the spring generation. This division of 
families into a group of rapid development and into one of slower 
development, which leaps over a brood, has been frequently observed 
in nearly all the species by the entomologists of northern countries, 
and there is no doubt that it happens also very often in the south, 
where it explains also partial and suppressed broods. 
The bigenerates of the South of Europe nearly all remain such up 
to the latitude of central Mngland, simply reducing the length of their 
epoch of emergence, which are identical with those above recorded for 
the two northern broods of the triple-brooded. Only polychloros is 
already reduced to one single annual cycle in the whole of the British 
Isles. The fact is worth noting that on the contrary urticae succeeds 
in very mild autumns in producing a small number of individuals in 
October, because some of those of the brood of August-September, 
instead of preparing to winter, copulate and produce progeny ; thus 
the third partial extraordinary brood winters consequently together 
with the second brood, and together with a few individuals from the 
first brood of June, who retire to winter and fall into lethargy for ten 
months until the following April. All this shows what an extra- 
ordinary power of adaptability, and what great resources, are possessed 
by Lepidoptera to adapt themselves to different meteorological condi- 
tions and to survive even sudden changes, which to them must be 
catastrophic ! 
In England the annual species follow the same rules as those 
mentioned with regard to altitude: the spring species emerge every 
year according to the climatic conditions, owing to which a precocious 
species like curdamines can be delayed until June when the winter is 
prolonged, or crataegi until July; the species proper to June in Italy 
emerge normally in July or at the beginning of August; the species of 
