APPENDIX 485 



pharynx), thyroid (probably), oesophagus, stomach, lungs, liver, 

 pancreas, intestine and rectum. The various sections of the gut are 

 characterised by the same histological peculiarities as in the normal 

 animal, e.g. ciliation of the oesophagus and typical glands in the 





i %Fi 



a 



Fig. 217 



Self-differentiation in exo-embryos, axolotl. Extrusion of yolk-cells, a, in normal 

 embryo, into lumen of gut ; b and c, in exo-embryos, from the surface. (From 

 Holtfreter, Arch. Entwmech. cxxix, 1933.) 



stomach. Perhaps the most remarkable self-differentiation is that 

 of the small intestine. In the normal axolotl larva of a certain 

 definite age, a number of yolk-rich tells belonging to this region 

 partially degenerate and become detached into the lumen and are 

 subsequently digested by the remainder of the epithelium (fig. 217). 

 In the exo-embryos, this same process of degeneration and detach- 



