Ill 



DIFFERENTIATION 



75 



maturation and, in some instances, fertilization, the experi- 

 ments just reviewed demonstrate the necessity of the parts of 

 this structure for the development of organs of the embryonic 

 body ; removal of this or that part entails the absence of this 

 or that organ. The materials therefore on which the forma- 

 tion of these organs depends may be said to be preformed in 



ms 



m'ch. 



m'ch 



FIG. 16. Cynthia partita. Half and three-quarter embryos. (After 

 Conklin.) a, right half gastrula, dorsal view. The neural plate, chorda, 

 and mesoderm cells are present only on the right side and in their 

 normal position and numbers, b, left half of young tadpole, dorsal 

 view. The notochord is normal except for size and number of cells ; 

 the muscle and mesenchyme cells are present only on one side ; the 

 neural plate (n.p.} is abnormal in form but not in position, c, right 

 half of young tadpole, dorsal view ; slightly younger than b. m'ch., 

 mesenchyme, ms., muscle-cells, d, left anterior three-quarter embryo, 

 dorsal view. The anterior half is entirely normal with anterior mesen- 

 chyme (m'ch.} on both sides. Posterior mesenchyme and muscle-cells 

 upon the left side only. 



