434: HYBERNATION. OF. INSECTS. 
reward the votaries of entomology, is afforded by the 
coincidence between the period of the hatching in spring 
of eggs deposited before winter, and of the leafing of the 
trees upon which they have been fixed, and on whose 
foliage the larvae are to feed: which two events, requir- 
ing exactly the same temperature, are always simultane- 
ous. Of this fact I have had a striking exemplification 
the last spring (1816). On the 20th of February, ob- 
serving the twigs of the birches in the Hull Botanic 
Garden to be thickly set, especially about the buds, with 
minute oval black eggs of some insect with which I was 
unacquainted, I brought home a small branch and set it 
in a jar of water in my study, in which is a fire daily, to 
watch their exclusion. On the 28th of March I obser- 
ved that a numerous brood of Aphides (not 4. Betwe, 
as the wings were without the dark bands of that species) 
had been hatched from them, and that two or three of 
the lower buds had expanded into leaves, upon the sap of 
which they were greedily feasting. This was full a 
month before either a leaf of the birch appeared, or the. 
egg of an Aphis was disclosed in the open air.—To view 
the relation of which I am speaking with due admiration, 
you must bear in mind the extremely different periods at 
which many trees acquire their leaves, and the conse- 
quent difference demanded in the constitution of the eggs 
which hybernate upon dissimilar species, to ensure their 
exclusion, though acted upon by the same temperature, 
earlier or later, according to the early or late foliation of 
these species. There is no visible difference between the 
conformation of the eggs of the Aphis of the birch and 
those of the Aphis of the ash ; yet in the same exposure 
those of the former shall be hatched, simultaneously with 
