THE INCUBATION OF SERPENTS. 349 



subsequently, and took no heed of them whatever. Is it to be 

 taken as an indication that the first only were fertile, and that a 

 serpent possesses an instinct which impels it, when depositing 

 properly impregnated ova under circumstances unfavourable for 

 the development of the contained germ or embryo, to endeavour 

 to hatch them instead of leaving them to a fortuitous combination 

 of surrounding influences, as is undoubtedly the rule ? 



The matter is hardly susceptible of explanation on any 

 hypothesis, so far as I can see. Neglected eggs of this and other 

 species have recently been hatched over the warm tanks at the 

 Zoological Gardens, so that if we assume that infertile ova are 

 always disregarded, we must also admit that those which are 

 fruitful are sometimes deserted. I regret that I did not add the 

 immature and spoiled eggs to the group during the incubation, to 

 note whether the behaviour of the reptile would prevent any 

 variation when these were displaced. Again, the addition of 

 1*8° to the natural temperature in which these events took place 

 would not have been nearly sufficient to foster the necessary vital 

 processes in the egg ; yet that temperature could differ very little 

 from what such a snake would experience in its wild state at this 

 time of the year. And whether she forsook them in consequence 

 of disturbance, or because the heat of the boa's cage relieved her 

 of further responsibility in promoting their germination, is 

 equally a mystery ; I incline, however, to the latter view, as an 

 interval elapsed between the time of her removal to a new location 

 (the fact of which did not seem to disturb her) and the moment 

 of her roving. 



The reason of a serpent's occasional incubation has never 

 been satisfactorily demonstrated. We know, at any rate, that the 

 practice does not obtain among them as a rule, in a state of 

 nature ; we are justified in believing that such a process is quite 

 exceptional — we may indeed doubt whether it ever occurs at all. 

 Even the evidence of the reptile's defending its nest is meagre and 

 dubious. In tropical countries the eggs are usually laid on the 

 damp sand, or in marshy jungle, and left without further care to 

 the vivifying influence of the sun ; in colder climates they are 

 extruded in manure-pits, hot-beds, heaps of dead leaves and other 

 decaying vegetable matter where heat is generated by fermentation, 

 or in accidentally warm situations ; but in both instances one 

 often finds such a deposition without a trace of the snake's recent 



