2 :^^al•y Blount. 



Tlie SesiiK'ntiitioii (":ivil.v in the pi.ixcon's cks" is hoinologons with that 



of other vertebrate egj?s 48 



VI. Tht> I'eriblast of the Bird's E^jl; compared with the vegetative pole of 



holohlastio vertebrate eggs 49 



►Smmiiary 52 



Literature 58 



Intkoductioa^. 



The history of the early development of the bird's egg has been 

 obscure because of the difficulty of obtaining abundant material in 

 a close series of consecutive stages. On account of the regular egg 

 laying habits of pigeons and because they breed readily in con- 

 finement, they offer invaluable material to the student of bird 

 embryology. 



The pigeon lays two eggs. The first is laid about 4.30 or 5.00 

 o'clock in the afternoon. About eight o'clock in the evening of the 

 same day the second egg leaves the ovary and is fertilized at that 

 time. It is laid about 1.00 or 1.30 p. m. of the second day following 

 the time of laying of the first egg; that is, it is laid about forty -one 

 hours after fertilization. It is evident that after the first egg is 

 laid, the pigeon may be killed and the second egg obtained in any 

 desired stage. 



These facts were published by Dr. E. TI. Harper ('04) in his 

 thesis on ''The Fertilization and Early Development of the Pigeon's 

 Egg." In regard to ovulation, Dr. Harper says (p. 352), "In all 

 cases observed, this has taken place between seven and nine o'clock." 

 In this paper I shall refer to eight o'clock in the evening as the 

 ai)proximate time of fertilization, although the exact time for any 

 particular egg is not known. 



Some of the results of my research were published in a preliminary 

 paper in the Biological Bulletin, October, 1907. 



For this research, one hundred and forty-four eggs have been 

 obtained, covering the period required for the egg to pass through 

 the oviduct. Of these, there is an egg for every hour, with more 

 abundant material at critical stages. The present thesis refers 

 especially to the first fifteen hours after fertilization. Problems 

 in later oviducal development are reserved for publication at some 

 future time. 



