Intestinal Epithelium of Bufo Lentiginosus. 265 



obstetricans, and Duesberg reports that Rana fusca shows complete 

 agreement with these conditions. The phenomena are essentially 

 the same in Bufo lentiginosus. I shall refer only briefly to a few 

 points brought out by the method used in studying Bufo. The 

 employment of subnitrate of bismuth and the X-rays was sug- 

 gested to me by Cannon's paper ('02) in which he describes its use 

 in his physiological work upon the movements of the intestines of 

 the cat. By employing this method with Bufo it has been possi- 

 ble to figure successive changes in the same individual from day 

 to day, and the danger of displacement by dissection is done away 

 with. Also the exact time at which the larvae begin to take food 

 is easily determined. With animals reared under normal condi- 

 tions (20° C), this occurred on the sixth day after hatching (Fig. 

 1), which corresponds with the time of rupture of the stomodeal 

 septum. 



This series, exposed first upon the sixth day, was subjected to the 

 X-ray eight times. These rays had no effect upon development or 

 metamorphosis, as could be determined by comparison with control 

 larvae. 



The coil of the small intestine increases in length until a maxi- 

 mum is reached at a time when the hind legs are well developed, 

 but not yet drawn up on the body (earlier than Fig. 3). The short 

 oesophagus is followed by the stomach and duodenum, which lie on 

 the extreme right side and dorsal to the large coil. The rectum lies 

 on the left, also dorsal in position. 



As Yung and Babak have shown experimentally, the extreme 

 length of intestine in larval Anura is an adaptation to the plant- 

 eating habit — a difference of 58.15 per cent was obtained by Babak 

 ('06) in the length of intestine of two sets of larvse, one fed upon 

 plants, the other upon meat. As Ratner points out, the Urodeles 

 are meat eaters throughout life, and in Anura this plant-eating habit 

 is secondary. The change in adult Anura to meat eating and the 

 short intestine is a return to the normal. In the early differentia- 

 tion of the alimentary tract, two or three days after hatching, the 

 anterior part which is to form the stomach, lies in the normal position 

 for this organ in Vertebrates, on the left. There appears to be a 



