bird, as, for example, is found with the lapwing and the 

 domestic hen, or the killdeer and the hen. 



If size or bulk controlled the length of incubation, the 

 hen should have a much longer period of incubation than 

 that of the lapwing or killdeer, which, however, is not the 

 case. The domestic hen is much larger than any of the fol- 

 lowing species, lorikeet, pied-billed grebe and common tern, 

 yet all have almost identical incubation periods. 



Many birds are quite alike in size, yet exhibit marked 

 differences in their respective incubation lengths, i. e., 

 meadowlark and upland plover, kiwi and domestic hen. The 

 swift and the raven are recorded as having practically the 

 same incubation period, yet how great is the disparity of 

 their sizes ! This loose relation of size of bird and length 

 of incubation is more noticeable within the confines of 

 natural groups (families), the Buteonidae for example, a 

 fact which was pointed out by H. Milne-Edwards (38) as 

 long ago as 1863, and recently Cole and Kirkpatrick (92) 

 intimated their belief in such a relation in the pigeon family. 



While it is true that this connection between bulk and 

 incubation length is strikingly evident in some families, the 

 contrary obtains in many others, so that one can hardly con- 

 sider it a law. The lapwing is smaller than the wood-cock, 

 but has a longer incubation period, and with the Laridae it is 

 found that the sooty tern and the herring gull have similar 

 incubation periods, yet are markedly different in size. 



The body of at least one species of the Megapodidae is 

 about the size of a domestic hen, yet this species' incubation 

 period is twice as long as that of the hen. What shall one 

 say of the several races of song sparrows, with their marked 

 variations in size, and the incubation period of this species 

 (including the subspecies) ? It is highly improbable that 

 the differences in these sizes are paralleled by differences in 

 the incubation lengths. 



It is impossible to explain or understand the situation 

 which arises in considering the record of the lammergeier, 

 the incubation period of which is given as twenty days ; this 

 species is larger than the golden eagle (159), and its short 

 incubation period (as recorded) is inexplicable under any 

 given theory (past or present) , and the writer believes the 

 record is incorrect. 



It would seem from the above examples that there is 

 too much lack of concordance between the bird's bulk and 

 its incubation period to admit a controlling relation of the 

 first over the second, even admitting that there is a loose 

 relation between the two. 



If now one assumes that by size of bird is meant weight, 

 one has a more stable standard to go by, especially if one 

 assume certain criteria as necessary in taking the weight. 



