150 GENERAL BIOLOGY. 



(g) The aortic arches. What is their relation 



to the pharynx ? 

 (h) The optic vesicles. 

 (i) The amnion. 

 Sketch six different regions. 

 VI. The Third Day. 



1. Surface. 



Note the curvature of the embryo; upon 



which side does it lie ? 

 Note the cranial flexure. 

 Review the structures seen in the second day 



and observe their further development. 

 New structures : 

 (a) The anterior vitelliue vein. What is the 



course of the blood within it ? 

 (6) The gill-slits. 



(c) The lens of the eye. 



(d) The nasal pits. 



(e) The allantois. (Possibly not yet visible.) 

 Sketch. 



2. Sections. 



Begin in the middle region (where the ar- 

 chenteron is still open). Make one sketch. 

 Then work backward into the tail-fold and 

 make out its structure completely. 



Find the section where the dorsal aortse pass 

 out into the area vasculosa. 



What is the origin of the allantois ? 

 A.t least two sketches desirable. 



