264 Mary A. Bowers. 



Material and Methods. 



The material used for this investigation has been our common 

 toad, Bufo lentiginosus, supplemented by the examination of many 

 series of the bullfrog, Rana catesbiana, and of the green frog, Rana 

 clamata. 



The most satisfactory fixing fluids were Flemming's and Zenker's. 

 Paraffin embedding was employed and sections cut 6 2/3 microns 

 thick. Considerable difficulty was experienced in cutting the first 

 series, especially the young stages, owing to the diatoms and sand in 

 the intestine. This trouble was avoided by feeding the tadpoles for a 

 day before killing, on fine yellow corn meal, which replaced the 

 gritty contents. A long series of substances, flour paste, egg (yolk 

 and white), beef juice gelatine, and meat were tried, but were not 

 satisfactory. 



The Flemming material was stained with Heidenhain's iron 

 hsematoxylin and orange G. Delafield's hsematoxylin (in toto) and 

 eosin (on the slide) were used for the larvae preserved in Zenker. 

 All figures were drawn with the aid of an Abbe camera lucida. The 

 photomicrographs were taken with violet light. 



Living tadpoles were used for all X-ray photographs except Figs. 

 3-10 ; these were taken from preserved specimens whose alimentary 

 tracts contained only the normal food. Larvae were prepared for 

 all other photographs in the following way: subnitrate of bismuth, 

 a non-irritating powder and insoluble in water, was placed in a 

 flat-bottomed glass dish and the tadpoles allowed to feed on it for four 

 or five hours. Larvae which are not transforming feed almost con- 

 tinuously, by night as well as by day, so the whole canal is kept 

 well filled. They were then placed in a 5 per cent solution of ether 

 and when quiet (usually in about 15 minutes) they were taken out 

 and arranged on a thin piece of paraffin paper, to protect the X-ray 

 plate, and exposed to the rays for thirty seconds. The animals were 

 immediately replaced in pure water where they revived in from 

 5 to 10 minutes. 



Mackoscopic Changes.. 



Renter, in the first part of his work, describes the gross changes 

 which occur during metamorphosis, in the alimentary tract of Alytes 



