POISONOUS SNAKES OF NORTH AMERICA. 397 



quarters, spreading out over the ueigbboriug region and passing the 

 summer solitary or in pairs. In very hot and dry (climates this hiberna- 

 tion has at I equivalent in the aestivation, by which term Dr. Cooper 

 has designated a similarly lethargic state during the hottest and driest 

 portion of the summer. 



Considering the small number of these snakes met with in the fields 

 or in the woods during the warm seasons, the large numbers some- 

 times found in these Eattlesuake dens in winter is simply astounding. 

 It seems as if all the pit vipers of the surrounding country had come 

 together in one spot, and there are good reasons to suppose that so is 

 actually the fact. The question naturally arises: How have all these 

 snakes obtained their information about this api>arent place of rendez- 

 vous and how have they been able to find their way to it? It is a 

 phenomenon in its nature not unlike that of the migration of birds, 

 and IS apparently even more difticult of a satisfactory explanation. 

 The old i)re-darwinian conception of the inherent and infallible instinct 

 explains neither, but how is the more scientific idea of the inherited, 

 unconscious knowledge accumulated and crystallized, as it were, dur- 

 ing countless generations, how is it to apply in the present case? 



As a matter of fact we know yet too little ot the habits of the snakes 

 and of their whole life history to give any explanation much better 

 than a conjecture. I shall, therefore, not attempt any solution of the 

 question here, but for the benefit of those who might want to take it 

 up I shall quote an ingenious theory proi)Ounded recently by Mr. W. H. 

 Hudson,* whose charming ijictures of animal life in the Argentine 

 Republic has made his name a household word among naturalists. 

 After having briefly alluded to the habit of the rattlesnake to hiber- 

 nate socially in dens, he proceeds as follows: 



Clearly in this case the l\uo\Yle(lgo of the hiberuating deu is not merely tradi- 

 tional — that is, handed down from generation to generation, throngh the young each 

 year following the adults, and so forming the habit of repairing at certain seasons 

 to a certain place — for the young serpent soon abandons its parent to lead an inde- 

 pendent life; and on the approach of cold weather the hibernating den may be a 

 long distance away, 10 or 20, or even 30 miles from the spot in which it was born. 

 The annual return to the hibernating den is then a fixed unalterable instinct, like 

 the autumnal migration of some birds to a vvarmer latitude. It is doubtless favor- 

 able to the serpents to hibernate in large numbers massed together, and the habit 

 of resorting annually to the same spot once formed, we can imagine that the indi- 

 viduals — perhaps a single couple in the first place — frequenting some very deep, dry, 

 and well-sheltered cavern, safe from enemies, would have a great advantage over 

 others of their race; that they would be stronger and increase more, and spread 

 during the summer montlis fartlier and farther from the cavern on all sides, and 

 that the farther afield thej" went the more would the instinct be perfected, since all 

 the young serpents that did not have the instinct of returning unerringlj' to the 

 ancestral refuge, and that, like the outsiders of their race, to put it that way, merely 

 crept into the first hole they found on the approach of the cold season, would be 

 more liable to destruction. 



^The Naturalist in La Plata (London, 1892), pp. 321-322, 



