158 



LIFE. 



inactive state, their normal constitution would 

 be soon affected by their proneness to de- 

 composition, and their peculiar properties be 

 consequently lost. Amongst cold-blooded ani- 

 mals, however, we find instances of more com- 

 plete suspension of vital actions, which may 

 even be prolonged for a considerable period. 

 Thus, Spallanzani kept frogs, salamanders, and 

 snakes, in a torpid state, in an ice-house, where 

 they remained three years and a half, and rea- 

 dily revived when again exposed to the influ- 

 ence of a warm atmosphere. Insects, in their 

 pupa state, may be regarded as analogous to 

 plants reduced to bulbs. Although the dura- 

 tion of this torpid condition is ordinarily deter- 

 minate for each species, and although some 

 changes occur during its continuance which 

 scarcely warrant us in characterising the state 

 as one of entire inactivity, there are some in- 

 stances which prove that it may be prolonged 

 for an almost indefinite period, under particular 

 circumstances. The degree of temperature to 

 which pupae are exposed seems to have the 

 same kind of influence over them as on the 

 eggs of insects. Thus Reaumur found that 

 pupiE, which would not naturally have been 

 disclosed until May, might be caused to un- 

 dergo their metamorphosis in a fortnight during 

 the depth of winter, by the influence of artifi- 

 cial heat; and, on the other hand, that their 

 change might be delayed a whole year beyond 

 its usual time, by the prolonged influence of a 

 cold atmosphere. We can scarcely imagine, 

 however, that temperature is the sole agent in 

 accelerating or retarding the final metamor- 

 phosis. If the caterpillar of Pupilio Machu- 

 on, one of those which has annually a double 

 brood, becomes a pupa in July, the butterfly 

 will appear in thirteen days ; if not until Sep- 

 tember, it will not make its appearance until 

 the June following, that is, not in less than 

 nine or ten months. Here it is evident that the 

 torpor has been prolonged from some cause in- 

 herent in the system itself, for the purpose of 

 preventing the disclosure of the butterfly at too 

 early a period of the season. A still more cu- 

 rious proof of this tendency to prolonged tor- 

 pidity during the pupa state is the following. 

 If a number of the pupae of the Eriogaster 

 lanestris, a moth whose larvae are common on 

 the blackthorn in June, be selected at the 

 same time, and placed in the same circum- 

 stances, the greater number of them will dis- 

 close the perfect insect in the February follow- 

 ing ; some not until the February of the year 

 ensuing; and the remainder not before the same 

 month in the third year. The same has been 

 observed of the Arcica mcndica, of which 

 thirty-six pupae, grown from eggs laid by the 

 same parent, produced twelve perfect insects in 

 each of the three following seasons.* The// 

 cause of this curious tendency may be, as sur- 

 mised by Mr. Kirby, to secure the race from 

 being cut off by unfavourable seasons, or by 

 some extraordinary increase of its natural ene- 

 mies. But its efficient cause can only be looked 

 for in some modification of the properties of 



* Kirby and Spence's Entomology, vol. iii.'p. 266. 



the organism analogous to that which produces 

 the phenomena of hybernation in other animals. 

 The same periodicity, manifesting itself, not in 

 obedience to a diminished temperature, but at 

 the season of greatest heat, is observed in tro- 

 pical climates. Many tribes of insects in the 

 torrid zone seem to retire to places of retreat 

 during the parching droughts of summer, and 

 make their appearance again during the rainy 

 season, when vegetation is in the highest luxu- 

 riance. We here trace the same beautiful 

 adaptation of the phases of animal and vege- 

 table life as in the former instances ; but the 

 efficient cause which induces these changes 

 must be different. 



Our limits do not allow us to dilate upon 

 one very interesting department of this subject 

 the prolongation of dormant vitality under 

 particular circumstances in frogs and other 

 reptiles. Many marvellous stories of this kind 

 are on record ; such as the inclosure of these 

 animals in solid blocks of granite or other 

 igneous rocks, which no well-informed person 

 can credit. There are, however, a sufficient 

 number of authentic cases to prove, in the esti- 

 mation of those who have fairly examined 

 them, that toads and other reptiles may be en- 

 closed in masses of rock apparently solid, or 

 in the substance of the trunks of trees, and 

 that they may preserve their vitality under such 

 circumstances for a very long period. In the 

 former instances, it would appear that the ani- 

 mal has fallen into a chink or crevice, which 

 has been gradually filled up by the washing-in 

 of gravel or other materials disposed to soli- 

 dify ; and that thus the appearance of a solid 

 mass has been given, when in reality some com- 

 munication has existed between the cavity and 

 the external air. It is by no means impossible, 

 moreover, that these animals might be found 

 imbedded in the sandstones at present in 

 course of formation in many localities ; these 

 rocks possessing considerable hardness, but 

 being at the same time sufficiently porous to 

 allow of the slow passage of air through their 

 substance. Where toads have become im- 

 bedded in crevices of trees, and been sur- 

 rounded by new layers of wood, it is evident 

 that a direct communication with the atmos- 

 phere will probably exist by means of the ori- 

 ginal crevice, although it may be much nar- 

 rowed ; but even if this be not the case, the 

 porosity of the wood will furnish the required 

 condition. Some amount of access of air 

 would seem, from the experiments of M. Ed- 

 wards and Dr. Buckland, to be essential to the 

 prolonged vitality of toads enclosed in solid 

 masses ; and this will probably maintain a very 

 feeble respiratory action upon the blood through 

 the general surface, just sufficient to prevent 

 the decomposition of the body. Vital action 

 cannot, therefore, be regarded as so completely 

 extinct under these circumstances as in some 

 of the cases formerly mentioned, where the ap- 

 plication of cold lias not only completely 

 checked it, but has also done away with the 

 necessity for it, by completely subduing the 

 tendency to decomposition. 



In the human economy, as in that of other 



