NEURAL TUBE 



BLOOD CLOT 



MOIST CHAMBER 



BRAIN 



Fig. 83. The origin of the nerve 

 fiber from a single neuroblast. At 

 the upper left an operation on a 

 young frog embryo is diagramed. 

 The heavy black region represents a 

 small section of the neural tube. In 

 the upper right, the section of the 

 neural tube is shown within a blood 

 clot, which fixes the tissue to a glass 

 cover slip. The cover slip is sealed 

 over a depression in a glass slide so 

 that the preparation remains sterile 

 and moist. At the lower left a mag- 

 nified view of the preparation shows 

 the migration of cells. The behavior 

 of one of these cells is diagramed 

 in the lower right. An amoeboid 

 outgrowth moves through the blood 

 clot and comes in contact with an 

 obstacle. The outgrowth turns and 

 follows this obstacle. When it leaves 

 the obstacle it follows a devious 

 path and may branch to form two 

 cones of growth. 



NEUROBLAST 



0B3TACLE 



CONE OF GROWTH 



143 



