12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ^2 



incubating. This is true also in the Recurvirostridae. In the case 

 of the herons definite knowledge is lacking so that I venture no state- 

 ment in regard to their sexual aberration in body temperature. 



Admitting that the incubation of eggs and the brooding of young 

 necessitate a higher temperature in the parent, it appears that in those 

 species where this duty falls upon the female she has a higher average 

 temperature than the male. Where the male performs these duties 

 the reverse is true. As in many cases, in particular among the pas- 

 serines, these cares are shared about equally by both parents, we may 

 expect in such species a close approximation in body temperature 

 in the two sexes, a supposition that is well borne out by the data given 

 in table 3. On the basis of this reasoning it may be permissible to 

 theorize further with regard to the shore birds. In many species 

 here the cares of the family are undoubtedly shared by both parents 

 though as has been said, in a good many forms this duty falls on the 

 males alone. However, in those that have been investigated, the 

 greater part show a higher temperature in males than in females. 

 In this group then, where the male is the home drudge taking over 

 all the family cares and leaving the female in freedom after the deposi- 

 tion of the eggs the condition may be assumed to be a primitive one. 

 Males of other species have become emancipated in part from this 

 domestic yoke so that the task of rearing offspring is shared in part 

 by their spouses, though this has occurred so recently that adjustment 

 is not complete and the body of the male still develops a higher 

 average temperature. Such statements however must be taken with 

 reserve and cannot be considered as applying to other groups of birds. 



EXTERNAL TEMPERATURE IN RELATION TO BODILY HEAT 



In the cold-blooded vertebrates heat generation within the body is 

 slow, while the processes that act in controlling radiation are imper- 

 fectly active. In consequence the animal chills or is warmed in close 

 harmony with fluctuations in heat of its surrounding element. Such 

 creatures of necessity are sluggish when they encounter low tempera- 

 tures and become more active when well warmed. When cooled below 

 a certain point they become torpid and dormant. It would seem that 

 animals of such habit have the means utilized in equalizing or resist- 

 ing high temperatures better developed than those that might assist 

 them in overcoming cold. Otherwise turtles, frogs, or lizards would 

 be killed when basking in the intense heat of a midsummer sun. This 

 equalization of heat must be accomplished largely by the lungs in 

 Reptilia, as skin glands that might serve this purpose are absent. The 



