CiiAP. I. DURATION OF LIFE. 89 



more strilving cxamplo of this peculiar mode of growth than the seventeen years 

 locust, so fully traced by Miss M. H. Morris.^ 



While all longlived animals continue, as a matter of course, their existence 

 through a series of years, under the varj-ing influence of successive seasons, there 

 are many others which are periodical in their appearance ; this is the case with most 

 insects,^ but perhaps in a still more striking manner with Medusa3.'' 



The most interesting point in this subject is yet the change of character which 

 takes place in the difforent stages of growth of one and the same animal. Neither 

 Vertebrata, nor MoUusks, nor even Eadiata exhibit in this respect any thing so 

 remarkable in the continuous changes which an individual animal may undergo, as 

 the Insects, and among them those with so-called complete metamorphoses, in which 

 the young (the larva) may be an active, woi-mlike, voracious, even carnivorous 

 being, which in middle life (the chrysalis) becomes a mummylike, almost motionless 

 maggot, incapable of taking food, ending life as a Avinged and active insect. Some 

 of these larva? may be aquatic and very voracious, when the perfect msect is aerial 

 and takes no food at all.* 



Is there any thmg in this regulation of the duration of life in animals which 

 recalls the agency of ph3\sical forces ? Does not, on the contrary, the fact, that 

 while some animals are periodical and bound to the seasons in their appearance, 

 and others are independent of the course of the year, show distinctly their independ- 

 ence of all those influences which, under a common expression, are called physical 

 causes ? Is this not further illustrated in the most startling manner by the extraor- 

 dinary changes, above alluded to, which one and the same animal may undergo 

 during different periods of its life? Does tliis not prove directly the immediate 

 intervention of a power capable of controlling all these external influences, as well 

 as regulating the course of life of every being, and establishing it upon such an 

 immutable foundation, within its cycle of changes, that the uninterrupted action of 

 these agents shall not interfere with the regular order of their natural existence? 



There is, however, still another conclusion to be drawn from these facts: they 

 point distinctly at a discriminating knowledge of time and space, at an appreciation 

 of the relative value of unequal amounts of time and an unequal repartition of 

 small, unequal periods over longer periods, which can only be the attribute of a 

 thinking being. 



' II.vuuis's InsecU injurious to Vegetation, p. 184. * Burmeister's Ilandb. d. Entom. etc. — L.VCOR- 



^ Hkrold, (E.,) Teutseher Kauijcn-Kalender, daire, Introd. ;i rEiitonuilogie, etc. — Kiiinv and 



Nordluui-sen, 1845. Spence, Introd. to Enlouiol., etc., q. a., give accounts 



• Agassiz's Acaleplis of North America, p. 228. of the habits of Insects during their metamorphosis. 



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