CHAPTER XVI. 



INFLUENCE OF THE SPERMATOZOA OF PIGEONS ON RATE OF 

 DEVELOPMENT OF THE EMBRYO.' 

 Crosses of those species of pigeons which have unequal periods of incubation 

 offer opportunities for the study of the separate influence of egg and sperm upon the 

 rate of development of the embryo which they conjointly produce. In other words, 

 such crosses give opportunity for the study of such a question as this: When a 

 cross is made between a female pigeon of a species whose incubation period is 14 

 days and a male whose species requires 18 days, will the incubation period of an 

 egg from such a pair be prolonged? If so, is the prolongation due to the influence 

 of the male? 



Table 178. — Normal incubation lime uf domestic pigeons. 



In this and succeeding tables the time determinations of much reliability and accuracy arc set in special type. — Editor. 



This subject has interested me for some time past, but for the present purpose I 

 have just had time to collect the data, and I give them without having had much 

 time to reflect upon them. My study of the subject is not yet concluded. = In this 

 investigation it is necessary to learn the normal incubation time of the species used 

 in the crosses and then the incubation period for the germs which represent the 

 cross. In the common dove {Colnmha domestica) the result of all the tests I have 

 made till now justify me in placing the incubation period for the first egg of the 

 clutch at 18 days and for the second egg at 17 days (table 178). In determining the 



' Stenographic report (slightly corrected by the author and adapted by the editor) of a lecture to the Zoological 

 Club, The University of ChicaRO, March 9, 1898. 



' The results of later studies have been incorporated in this chapter. — Editor. 



