OUTLINE FOR LABORATORY STUDY OF THE CHICK 333 



The head projects above the blastoderm. The fold which unites 

 the ventral surface of the head with the blastoderm is called the 

 head fold. 



The diverging folds of the myelon encloses the primitive streak. 



On each side of the neural tube are the mesoblastic somites. The 

 series is continued behind by the undivided segmental plate. 



The heart is beneath the hindbrain. The portion of the body 

 cavity in which it lies, is bounded in front by the head fold and behind 

 by the diverging limbs of the splanchno-pleure. Its posterior or 

 venous end receives the vitelline veins from the vascular area. The 

 anterior or arterial end is prolonged into the ventral aorta. 



Note that the axis is somewhat bent. 



The head fold of the amnion is noted to extend over the anterior 

 end of the head. 



A study of the transverse sections. * 



The sections about 20 micro-millimeters thick should be cut serially, 

 and so mounted. Knowing how many micro-millimeters the 

 embryo is in length will enable one to make a diagram of the fetal 

 structure in the study of the series of transverse sections. The 

 sections should be drawn in the order studied so as to obtain relative 

 structural ideas. 



With the microscope study the following regions: 



1. Optic vesicle. 



2. Midbrain. 



3. Posterior half of the heart. 



4. Myelon in the closed region. 



5. Myelon in the open region. 



6. Through the primitive streak. 



2 . THE EMBRYO TWENTY TO TWENTY-FOUR HOURS OLD WITH FROM 



TWO TO six SOMITES". 



Compare the parts in this embryo with those of the embryos from 

 twenty-nine to thirty-four hours old. Note and describe the rela- 

 tions of the embryo, the area pellucida, and the area opaca. Note 

 how much of the yolk the blastoderm covers. 



In studying the entire embryos, note the condition of the medul- 

 lary plate. Observe if the tube is formed in any part; how far back 

 the head plate extends, if the heart can be seen; and if the primitive 

 streak is longer or shorter than in i. 



Study relations of structures and make drawings through the point 



