272 Mary A. Bowers. 



the arguments have already been fully set forth by him, also because 

 it is believed that the figures given in this paper offer their own 

 argument. 



It is probable that the significance of the histolytic and regenera- 

 tive phenomena which have been described in the three Anurans, 

 Alytes obstetricans, Rana fusca, and Bnfo lentiginosus, will be more 

 clearly seen when more extended work has been done upon other 

 forms, upon amphibia in general. 



It appears from the comparative work which has already been 

 done that in the tadpole of Anura we have merely a temporary adap- 

 tation, and, as in the case of the larvae of those insects which undergo 

 complete metamorphosis, that these conditions have no phylogenetic 

 significance. 



Experimental Wokk. 



I. Mechanics of the early differentiation of the alimentary canal. 



Text figure A shows the successive changes which had occurred in 

 one individual of Rana palustris by the second, third, fourth and 

 sixth days after hatching. Rana palustris was used because the lack 

 of pigmentation at this stage allows one to see clearly, without dis- 

 section, the changes in the alimentary tract. Dissection of different 

 individuals of Bufo on successive days indicates that the changes are 

 the same as in Rana palustris. 



Text figure A, I, shows the oesophagus, stomach, anterior part of the 

 duodenum and the rectum formed; the rest of the tract is an un- 

 differentiated mass of yolk from which the coil will be formed. The 

 stomach lies on the left side, in the normal adult position. Further 

 growth, i. e., differentiation of the coil, takes place in the region 

 marked x, and because of this vigorous growth, the stomach and duo- 

 denum are crowded into the temporary larval) position on the right. 

 Theoretically this transfer from the left to the right side would 

 appear to be due to a passive crowding, not to an active movement of 

 the anterior part of the digestive tract, for the cellular structure of 

 this region is already laid down in the stage shown in I. 



To test experimentally this question of crowding, that is, whether 

 the stomach would remain on the left if the coil did not usurp its 



