36 



Mary Blount. 



(l-f-2) parallel to the axis of the embryo^ hut in an excentric 

 position. In another egg (Egg 420, Fig. 16 A) in which I watched 

 the development, there was one cleavage plane (l-j-S) visible at 

 2.15 a. m. and it was transverse to the axis of the future embryo. But 

 these lines are not constantly in view. As the blastomeres of the 



Fig. 16. — Two views of a living pigeon egg. A was drawn at 2.15 a. m., 

 six and one-fourtli liours after the estimated time of fertilization. B was 

 drawn about forty-five minutes later, between 2.50 and 3.05 a. m. 



living egg separate from each other, the furrow between them is 

 widened and is then easily seen. But when the cells press closely 

 together, the cleavage furrow fades from view. Thus it may be 

 that when I first saw Egg 404 (Fig. lY) the plane 3 + 4 may have 

 heen temporarily invisible, but may have been really the first cleavage 

 furrow, and 1+2 the second. 



