CURIOUS FACTS ABOUT CIIRYSALmS. 1557 



if another stage be stiicliecl, wo find at once where selection lias been em- 

 ploying her forces and can only regard the differences here as marks of an 

 immense lapse of time since the common ancestor of all flourished upon 

 the earth. 



liut to leave these general considerations and to return to our ehrysalids. 

 We have pointed out some common features of interest about their struc- 

 ture. Can we find anything worthy of remark in the life of such api)ar- 

 ently lifeless things? Certainly ; we may fairly call a chrysalis a most 

 tickle objei't ; a most uncertain creature. Has it not been mentioned over 

 and over again in tiiis work that while one brood may follow another with 

 tolerable regularity, broods are very apt to be uneven in their numbers, 

 because some ehrysalids fail to disclose their inmates at the expected time 

 but wait a little or a longer time ? That there should be some little vari- 

 ation due perhaps to conditions of temperature were to be expected ; but 

 that the continence of the chrysalis sliould be just enough to have it skip 

 a brood is certainly reason for wonder, for here meteoric conditions can 

 often have clearly nothing to do with it. Some instances, indeed, are on 

 record where, when normally a single winter would mark the duration of 

 a chrysalis, it has lasted two winters and, of course, the intervening sum- 

 mer. All these variations seem to be provisions of nature to guard against 

 destruction of the species under adverse circumstances. Nature seems 

 always on her guard. 



Or take a kindred fact. It is well known to tlie aurelian that the males 

 of a given brood almost invariably make their appearance before the fe- 

 males, sometimes only a day or two, sometimes as many weeks. It seems 

 only another instance, so many of which are known in both animal and 

 vegetable kingdoms, of a device to secure fertilization. Now, Mr. Ed- 

 wards, with his unrivalled experience in breeding butterflies, tells us, what 

 all of us have seen on a smaller scale, that when bred in confinement, not 

 exposed to all the vicissitudes of the weather, the females appear quite 

 as early as the males. What subtle influence then is it which earlier 

 awakes the male under wholly natural conditions ? 



We owe to Wilhelm iliiller (a brother of Fritz Miiller, who has made 

 so many neat observations in the natural history of tropical animals) a 

 curious fact in the lives of the free hanging ehrysalids of tropical Nym- 

 phalidae. Every naturalist knows how rarely these ehrysalids are dis- 

 covered in free nature ; most of our knowledge of them comes fi'om those 

 raised in confinement ; for the caterpillar nearly always seeks an obscure 

 place in which to change or else imitates in its color and perchance in its 

 form, surrounding oljjects. Now ^liiller has discovered that many of 

 them are directly sensitive to light and will respond, slowly indeed but 

 eflTectually, to its presence. To exi)erimeut upon them he devised an ar- 

 rangement by which the light — not the direct rays of the sun, but merely 



