CHICK, 68 TO 72 HOURS' INCUBATION 27 



c. Reconstructions 



1 i) The Circulatory System 







In your sections trace the circulatory system through 

 several times. Make outline drawings of the blood 

 vessels in about every third section. Make all your out- 

 line drawings on the same scale, keeping the relative 

 position and shape that are seen in the sections. Keep 

 your drawings in consecutive order. 



From your drawings make a diagram of the circulatory 

 system of the forty-eight-hour chick and label all the parts. 



What changes have taken place in the circulation 

 between the thirty-six-hour chicken and the forty-eight- 

 hour chicken? 



(2) The Central Nervous System 



Trace the central nervous system through several 

 times. Make outline drawings of every third section of 

 it. Think of these sections as having a definite thickness 

 and placed one upon the other in regular order. 



Make a diagrammatic drawing of the central nervous 

 system and label all the parts. 



4. Embryo with Thirty-five to Thirty-seven Mesoblastic 

 Somites (Sixty-eight to Seventy -two Hours' Incuba- 

 tion) 



a. Whole Mount 



It will be observed that the whole embryo is now lying 

 on its side. There is "another bend in the head region. 

 This bend is in the region of the hind-brain and is called 



