l66 • Edwin G. Conkltn. 



Right or Left Half or Three-Quarter Embryos; Gastrula to Tadpole. Drawn from 

 Fixed and Stained Material. 



Fig. 31. Right half gastrula of about 220-cell stage; spurted in the 4-cell stage and fixed 3 hours 

 later. The neural plate, chorda and mesoderm cells are present only on the right side and in their 

 normal positions and numbers. 



Fig. 32. Left half of young tadpole, dorsal view; spurted in the 4-cell stage, fixed 5 hours later. 

 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 is abnormal in form but not in position. 



Fig. 33. Right half of young tadpole, dorsal view; spurted in the 4-cell stage, fixed 4^ hours later 

 (slightly younger stage than Fig. 32). The notochord consists of a small number of cells which are 

 interdigitating; muscle cells and mesenchyme lie on the right side of the notochord, but not on the left, 

 though the muscle cells have begun to grow around to the left side; the neural plate is normal in posi- 

 tion but not in form. 



Fig. 34. Right-posterior three-quarter embryo, from the right side. The left anterior cells 

 (A^»', a*''') were killed in the 8-cell stage and the embryo fixed 5 hours later. The posterior half of the 

 embryo is normal, but the left half of the anterior part is lacking and the neural plate is abnormal and 

 has not formed a tube though sense spots are present. 



Fig. 35. Left-anterior three-quarter embryo, dorsal view; the right posterior quadrant (B^) was 

 killed in the 4-cell stage and the embryo fixed 6 hours later. The anterior half of the embryo is entirely 

 normal. The muscle cells are lacking on the right side though they have begun to grow around the 

 hinder end of the notochord. The posterior portion of the trunk mesenchyme is found only on the left 

 side, but its anterior portion, which is derived from the cells A''-^ and A'^* (Fig. 6) of the anterior quad- 

 rants is present on both sides. In the region of the injured cell the notochord and neural tube are 

 curved away from that cell. 



Fig. 36. Left half embryo, from left side; spurted in the 4-cell stage, fixed 6 hours later. The 

 dorsal lip of the blastopore is being overgrown by the ventral (posterior) lip. Muscle cells and 

 mesenchyme are found only on the left side. The neural plate is abnormally folded, but still open; 

 sense spots are present. 



