ON GASTRULATION AND THE ORIGIN OF THE 



PRIMITIVE STREAK IN THE PIGEON'S 



EGG. — PRELIMINARY NOTICE. 



J. THOS. PATTERSON. 



The results of the experimental studies of Assheton ('96), 

 Miss Peebles ('98), and Kopsch ('02) on the primitive streak of 

 the chick demonstrate beyond any reasonable doubt that the 

 material of that structure enters into the formation of the embryo 

 — a view long held by many embryologists. In the light of these 

 experiments the opposite view of Balfour and his followers is no 

 longer tenable. The results obtained by these three workers 

 have, in the main, solved the problem of the fate of the primitive 

 streak, but they have not answered the question of its origin. 

 The present work was undertaken with the hope of throwing 

 light upon the latter question. It was soon found that its solu- 

 tion depended upon a morphological and experimental study of 

 stages occurring before the time of laying. The morphological 

 results mainly will be considered in this paper. 



Material and Methods. 

 It is doubtful if a more desirable material could be found for 

 the purposes of this investigation than that furnished by the 

 pigeon's egg. The regularity of the laying habits of the com- 

 mon pigeon makes it possible to secure eggs at approximately 

 any stage of development. Breeders have long known that this 

 bird ordinarily lays two eggs at a sitting, the first usually between 

 four and six P. M., and the second between one and two P. M., 

 on the second day following. According to Harper ('04) this 

 latter egg is fertilized at about eight P. M., just before it enters 

 the oviduct, and hence it is forty-one hours in traveling down this 

 passage. Thus, it will be seen that the investigator can secure 

 this second egg at approximately any stage of its early develop- 

 ment, for he needs but kill the bird at the proper hour and remove 

 the egg from the oviduct in order to obtain a desired stage. Eggs 

 removed in this manner, even as early as twenty hours before lay- 



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