24 THE SEMI-ANNUAL. 



3, Does the time occupied in building, or the material used, 

 differ at different seasons or in (Hfferent localities? 



4. Does the time of year affect the position of the nest with 

 respect to the Sun ? 



The question arises : How many of those questions are 

 answered in the foregoing report? With regard to the first ques- 

 tion I would say that it might easily be answered by a little pains- 

 taking labor. Mr. Bin-ns is the only one whose notes are full 

 enough to warrant me in taking his average of the size of eggs 

 as the average of his own locality, the others are too general to 

 be of use in this report. It will be seen by comparing Mr. 

 Burns's work with my own that there is no constancy of varia- 

 tion ; one species may show a larger average for Iowa and an- 

 other a larger for Pennsylvania ; hence no rule can be established. 

 It is true, hovv'ever, even though the reports throw no light upon 

 the subject that the smallest eggs come from the south, gradually 

 growing larger with every advance northward, with the most 

 northern the largest. That there should be some variation east 

 and west is, to my mind, highly probable, though the variations 

 would be less. In working upon this line of investigation, notes 

 east and west, should be studied and compared with the 

 isothermal always in mind. North and south are not in nearness 

 or remoteness to the poles, but in temperature, where the birds 

 are concerned. 



There is one thing more which may and probably does effect 

 the size of eggs in a set : the size of the set. Where only a 

 few are laid we would expect them to be larger and vice versa 

 in larger sets. Thus, in future reports, full notes should be sent 

 in, giving each set with its measurements by itself, with the date 

 and number of eggs in the set. 



The third question is answered affirmatively. Nests do differ, 

 both in materials used and in time in building, in different lo- 

 calities, if not at difierent seasons. This is seen in case of Wood 

 Thrush and Catbird especially ; it is true in a less measure of the 

 others. 



The second and fourth questions are still open as before. On 

 general principles we would say that the period of incubation 

 would probabl}' differ sou'ewhat at different seasons. The cold 

 causing a greater length of time for the development of the chick 

 than the warmer air of later Spring. * 



