METHOD OF OBTAINING EMBRYOS. 175 



gill-clefts showing externally. Embryos a little less or a little more developed are 

 almost equally serviceable. 



Removing the Embryo. Before the egg is opened a basin should be prepared 

 and filled with normal salt solution warmed to about 40 C. (104 F.). The basin 

 should be large enough to permit the entire egg to be submerged in it. 



Take the egg warm from the incubator or the hen; allow it to rest quietly in 

 one position for two or three minutes before opening it. This is in order to insure 

 that the side of the yolk which contains the embryo is turned uppermost. After 

 an egg is disturbed the yolk will turn and resume its normal position, for which 

 but a short time is necessary. The egg may now be held in one hand, the shell 

 cracked, and the pieces of the shell above the yolk be removed with forceps, mak- 

 ing a hole about an inch in diameter. The inner egg membrane may be removed 

 with the shell. If any of the white of the egg tends to overflow, it should be 

 immediately snipped off with a pair of scissors, otherwise it will cause the yolk 

 to roll over, thus concealing the embryo. 



The embryo and germinal area are now to be examined with the naked eye 

 or, better, with a hand lens. The student will detect very easily the area pellucida, 

 which lies at right angles to the long axis of the egg, and also see in the middle 

 of the area a long whitish streak, which marks the anlage of the embryo. Around 

 the area pellucida can be seen the mottled vascular area which will vary in ap- 

 pearance according as the development of the blood-vessels and blood-islands is 

 more or less advanced. The area vasculosa is , a portion of the larger area opaca 

 which merges at its periphery into the general yolk. In embryos of the second half 

 of the second day, thirty-six to forty-eight hours, the contraction of the heart can 

 be readily seen, and usually the outlines of the head of the embryo may be made 

 out. The germinal area is now to be separated from the rest of the yolk. To 

 accomplish this, plunge one blade of a sharp pair of scissors into the yolk a little 

 beyond the edge of the vascular area, and cut rapidly around until a circular inci- 

 sion has been completed; then take a flat .spatula and plunge it boldly into the 

 yolk at a depth of perhaps an eighth of an inch underneath the embryo. Next 

 lift out the embryo together with the yolk and the overlying white of the egg, 

 steady it a little if necessary on the spatula with a pair of forceps or needle, and 

 transfer it rapidly to the dish of warm salt solution. With a pair of fine forceps 

 the edge of the germinal area may be seized, and by gentle motion it may be 

 separated from the mass of yolk and also from the thin, whitish, overlying mem- 

 brane of the yolk, and at the same time from so much of the white of the egg 

 as may have been carried along. As one becomes more practiced in these opera- 

 tions, it is not difficult to remove the germinal area without taking much yolk 

 along with it. 



The operation may be modified as follows: After the shell is opened the egg 

 may be tilted so as to allow the white to run off, and as it runs over the edge 

 it is snipped through with the scissors, and as much of the white removed as is 



