350 Fertilization and Early Development of Pigeon's Egg 



certainly better adapted to furnish material for studies of this sort 

 than any other bird. 



About the early development of the large meroblastic eggs compara- 

 tively little is known. This has remained true in spite of the thorough- 

 ness with which the embryonic stages of selachian and chick have been 

 studied. As a result of the work of a number of investigators, chiefly 

 Riickert, there is now a fairly complete general survey of the fertilization 

 and early stages of the selachian egg. Observations upon the early 

 development of the bird's egg are very few. Some of the early cleavage 

 stages of the chick were figured by Coste, and Balfour contributed some 

 observations. The internal phenomena of the egg during maturation, 

 fertilization and early cleavage have remained an open field for investi- 

 gation. 



Upon the ovarian history of the bird's egg observations have been 

 quite numerous. The paper of Holl, 90, upon the hen's egg may be 

 mentioned as one of the most important. 



The development of the large meroblastic eggs obviously presents 

 numerous problems. In this paper the stages of the egg obtained are 

 scattered over a considerable period, and present glimpses of various 

 phases of maturation, fertilization and early cleavage. A few stages 

 of the ovarian egg have also been introduced. 



Methods. 



The method followed has been to fix the whole egg before attempting 

 to remove the germinal area. The oviduct is removed, the position of 

 the egg being carefully noted, as this enables one to judge the approxi- 

 mate stage in development and determines the subsequent treatment in 

 staining. The portion of the oviduct containing the egg is then cut off, 

 immersed in the fixing fluid and slit open underneath the liquid. In 

 case of an egg which is free in the body cavity, with some caution the 

 body may be inverted over the fixing fluid, allowing the egg to drop 

 out. The large ovarian egg may be fixed long enough to allow the fluid 

 to penetrate the disc, then hardened in alcohol and the germinal area 

 subsequently dissected out. 



The choice of fixing fluids is somewhat limited, since many of them 

 leave the disc too brittle to stand the subsequent treatment, and washing 

 in water is undesirable. The picro-acetic mixtures have been chiefly 

 used. Long fixation is not necessary or desirable, owing to the swelling 

 of the yolk, which is apt to distort the disc. 



'It is well to cut out a considerable portion of the surrounding yolk 

 with the disc and then to float this piece into a shallow watch-glass and 



