EMBRYOLOGY. 147 



(/) The urn in the centre, its neck extend- 

 ing to the blastoderm. 



(g) The alternate layers of white and of yel- 

 low yolk. 

 Diagram 1 



In the following work the students should 

 leave the slides in the trays on their tables 

 at the end of the laboratory period. If a 

 particular slide is wanted again, its number 

 should be entered by the student on the 

 card that is hanging up for the purpose. 



II. The Unincubated Blastoderm. 

 Examine first tvith A A 2, then with D 2. 



1. Surface view. Observe the relative size of 



the cells in the middle and at the periphery. 



2. Section. 



Sketch with D 2 the cell-outlines in a small portion 

 of (1) and (2) accurately, and on a large scale. 



III. The Early First Day. 



1. The primitive streak. Surface view. 

 Study with AA 2. Sketch carefully. 



2. The medullary folds. Surface view. 



Study ivith A A 2, then with D 2. Sketch carefully. 



3. Sections : 



(a) Primitive streak. (Single section.) 



(b) Medullary folds. (Single section.) 



(c) The early first day chick. (Complete 



series.) 



