376 C. M. Child 



pieces described above, but simply undergo reduction as in normal 

 animals. 



c Discussion 



In the case of the formation of a new postpharyngeal region 

 from a part of the old prepharyngeal region, or from the most 

 anterior part of the old postpharyngeal region, all parts of the 

 intestine except the longitudinal axial intestine degenerate com- 

 pletely in much less time than that required for reduction in nor- 

 mal animals. 



These cases present certain peculiar features: here the intes- 

 tinal material is present, but apparently for some reason the lateral 

 branches are unable to persist in the region which undergoes 

 redifferentiation. In later stages in the longer pieces small new 

 intestinal branches usually develop from the axial intestine in 

 the redifferentiated region. When the new postpharyngeal region 

 is formed from the anterior half or more of the old postpharyngeal 

 region, no such intestinal degeneration takes place. 



How are these peculiar phenomena to be interpreted .? The 

 hypothesis that the intestinal material of the redifferentiating 

 region is used up as nutrition for the growth of this region may 

 serve to account for the rapid disappearance of the products of 

 degeneration, but it does not serve to account for the degeneration 

 of the lateral intestinal branches alone, while the axial intestine 

 persists. Moreover, the process cannot be regarded in the light 

 of an adaptation, for it is certainly not economical of material and 

 energy, neither does it fit the animal better in any way for contin- 

 ued existence. On the contrary, it appears to be a useless destruc- 

 tion of structures of great importance, a waste of energy, and in 

 every way a process which must result to the disadvantage of the 

 animal. 



But when we consider these cases from the functional stand- 

 point they appear in an entirely different light. In the functional 

 redifferentiation of a part of the prepharyngeal region into a whole 

 postpharyngeal region certain changes in the mechanical condi- 

 tions must occur. After such redifferentiation contraction of the 

 body forces the intestinal contents in this region in the anterior 



