their Respiration, 119 



the first inhaled ; and, in coincidence with this opinion, we 

 must infer that the species with a single membrane respire in 

 the first instance the air behind it, and then, by their own 

 efforts, burst their prison wall. A very different explanation 

 of the process has been advanced by Sir Everard Home. He 

 says : — " When warmth and moisture are applied, the mem- 

 branous film (of the garden snail) falls off; a globule of air 

 that remained in the cavity of the lungs becomes rarefied, and 

 forces its w^ay out, and admits of fresh air being applied to 

 these organs."* {Comp, Aiiat.^ vol. iii. p. 156.) I suspect that 

 more of fancy than of observation enters into the baronet's 

 theory; for were the rarefaction of the contained air, and its 

 egress through the pulmonary aperture, all that was neces- 

 sary to shake off the winter slumber, this would be done on 

 several days in winter and in early spring, when the sun 

 shines brightly and the atmospherical temperature is high 

 enough to produce the effect, often higher, indeed, than it 

 is when they begin, in the appointed time, to leave their 

 hybernating retreats. If, says M. Gaspard, individuals of 

 Helix pomatia " were exposed during the winter to a dry 

 heat of from 60° to 100° for several days, or even weeks, 

 not one made its appearance; whilst, on the contrary, those 

 which were placed in a deep recess, the regular temperature 

 of which was 50°, came forth in April, or at the beginning of 

 May, without any increase of temperature." 



Dr. Turton, on the other hand, maintains that the doctrine 

 of Gaspard is equally untenable ; for that the direct commu- 

 nication between the external air and the animal within its 

 shell is never interrupted, but on the contrary preserved, by 

 means of a small aperture in the epiphragm. His words 

 are : — " But, upon examination, it will appear, that in the 



* In the following extract Sir E. Home repeats his hypothesis in a more 

 detailed manner : — "It is curious that, although respiration is necessary 

 for carrying on the functions of life, it is by no means so for the con- 

 tinuance of its existence. The garden snail illustrates this fact in the most 

 satisfactory manner. When the temperature of the atmosphere sinks 

 below a certain degree, this animal places itself upon a solid body, that it 

 may not be liable to fall off: it then forms an operculum of mucus, by 

 which respiration is stopped, and the animal remains hermetically sealed 

 up till warmth and moisture dissolve the mucus by which the animal was 

 fixed to its place ; and a globule of air retained in the lungs, which consist 

 only of one cell or bag, being rarefied, escapes externally, restoring the 

 communication with the air of the atmosphere which rushes in, and the 

 action of the heart is renewed. If it is admitted that the application of 

 oxygen to the muscles of the heart is capable of stimulating that organ, 

 nothing can be more simple than the mode in which this is effected : the 

 oxygen of the atmosphere is absorbed by the blood in the lungs, and the 

 closeness of the ventricle of the heart to the lungs permits the oxygen to 

 penetrate to the heart." (Comp. Anat.y vol. v. p. 129.) 



