spell than do those of birds, and they may bear, relatively 

 higher temperatures, i. e., the tuatara lizard's eggs 77 F. 

 (126) ; they probably remain viable for far longer periods, 

 their embryonic development persistently progresses at much 

 lower temperatures than does that of birds, and one would 

 predict, on these grounds, an exceedingly variable and elastic 

 apparent length of incubation, which is borne out by the 

 facts in the case. No reptile incubates its eggs, unless the 

 devoted care given by the female python to its eggs can be 

 so classed; this may, however, be a true but primitive kind 

 of incubation, a real beginning in the scale of incubation 

 habits, since it has been shown that a python's body tempera- 

 ture rises 10 F., above the surrounding air while covering 

 its eggs, and Heilmann (118) says the temperature of a 

 "quiet incubating snake" is about 50 to 53.6 F. If reptile 

 eggs respond to the same controlling influences as do those 

 of birds, it is possible that data on reptile incubation will 

 disclose such correlation; I have discovered a few facts, 

 which, while not nearly as numerous as might be desired, are 

 nevertheless quite suggestive. If I read aright, it appears 

 that the most primitive of all living reptiles is Sphenodon 

 punctatus, and on grounds outlined in this discussion, its 

 incubation period should be the longest of all living reptiles, 

 and it is, lasting from twelve to thirteen months, reckoning 

 from laying to hatching. It is necessary to recall, that about 

 five months of this period, extend over the New Zealand 

 winter, and that during this time the embryo ceases to de- 

 velop, and hibernates in ovo, as it were, until the environ- 

 mental conditions again become such that it can survive 

 when hatched.* 



The next longest period of incubation amongst reptiles 

 is that of the European tortoise (Emys orbicularis) which is 

 probably a higher reptile than Sphenodon, though it is 

 placed in an order ranked below that of the Sphenodon ; in 

 southern Europe the eggs of this tortoise hatch in five to 

 six months, w r hile in northern Russia (120), they require 

 eleven months; a large part of this eleven months is the 

 season of Russian winter, and during its intense cold, the 

 developing tortoise embryo is in a condition of suspended 

 animation yet, deducting this time from the whole period 

 of incubation, the actual developmental period is still next 

 to the longest amongst reptiles. Then comes the alligator, 

 and in this instance one is on secure ground in having a 



*It is possible that this reptile, which has persisted almost un- 

 changed since the Lower Permian, survived because it was able to 

 adjust, so to speak, its incubation to comparatively low temperatures, 

 which may have supervened in the course of geologic changes, and which 

 exterminated the then existing host of its huge contemporaries (dino- 

 saurs, etc.), whose probable long incubation periods required an equally 

 long period of relatively high temperatures. 



