^^ AND ^"^l-^ 



JOURNAL OF VARIATION. 



Vol. VII. No. 7. January 15th, 1896. 



Some Aspects of Hibernation. 



By F. A. DIXEY, M.A., M.D., F.E.S., Fellow of Wadham College, Oxford. 



The following remarks have been put together in compliance with 

 a request from Mr. Tutt for some expression of opinion on the sub- 

 ject of two recent papers, by himself and Mr. Kane respectively,*-* 

 dealing with the phenomenon of hibernation. 



Before making any special comment on the papers themselves, it 

 may be as well that I should clear the ground by offering a few con- 

 siderations on the general question. 



It is well known that in most regions of the globe all organisms 

 are subject to a periodical alteration of their environment, dependent 

 on the change of seasons. These variations of environment are in 

 the first place meteorological, the most important being changes in 

 respect of temperature and moisture. To each of such changes in 

 meteorological conditions every organism responds in its own charac- 

 teristic manner ; the modes of response differing in an almost endless 

 variety of ways, and being determined in some cases directly by the 

 influence of the new conditions on the organism itself, in others 

 indirectly through the effect produced on other organisms. For 

 example, in the temperate regions of the earth many trees lose their 

 leaves on the approach of winter. This effect may so far be con- 

 sidered a direct one, but it carries with it various indirect conse- 

 quences in respect of the life of insects which feed on the leaves, and 

 birds which feed on the insects. The interruption of the usual food- 

 supply is met sometimes by a change of diet, sometimes by a change 

 of locality (migration), sometimes by a suspension of bodily activity 

 (hibernation). Those observers who, with Darwin, see in natural 

 selection a sufficient cause for the transmutation of species, will have 

 no difficulty in attributing to the same agency the formation of the 

 various habits involved in the adoption of these several modes of 

 defence against the incidence of adverse external conditions. Under 

 the operation of natural selection, the change of habit will be an 

 entire or partial one according to the needs of the species ; it will 

 proceed by successive modifications of some already existing charac- 

 teristic, and it will also, of course, be limited in accordance with the 

 physiological possibilities of each several organism. Bearing these 



* " The Resting Habit of Insects as Exhibited in the Phenomena of Hiberna- 

 tion and ^Estivation." — Entomolo(jisV s Record, Vol. vii., 1895, p. 1; Ibid., p. 52. 



