HYBERNATION OP INSECTS. 



351 



have been fixed, and on whose foliage the larvae are to feed ; 

 which two events, requiring exactly the same temperature, 

 are always simultaneous. Of this fact I had a striking exem- 

 plification in the spring of 1816. On the 20th of February, 

 observing 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 un- 

 acquainted, 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 observed that a numerous 

 brood of Aphides (not A. betulce, 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 ap- 

 peared, or the egg of an Aphis was disclosed in the open air. 

 To view the relation of which I am speaking with due admi- 

 ration, you must bear in mind the extremely different periods 

 at which many trees acquire their leaves, and the consequent 

 difference demanded in the constitution of the eggs which hy- 

 bernate 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 the expansion of the leaves, nearly a 

 month earlier than those of the latter: thus demonstrably 

 proving that the hybernation of these eggs is not accidental, 

 but has been specially ordained by the Author of nature, who 

 has conferred on those of each species a peculiar and appro- 

 priate organisation. 



A much greater number of insects pass the winter in the 

 pupa than in the egg state ; probably nine tenths of the ex- 

 tensive order Lepidoptera, many in Hymenoptera, and several 

 in other orders. In placing these pupae in security from the 

 too great cold of winter and the attacks of enemies, the larvae 

 from which they are to be metamorphosed exhibit an anxiety 

 and ingenuity evidently imparted to them for this express 



