No. 2.] ENTERON OF AMERICAN GANOIDS. 427 



backward for a distance of 18 centimeters, where the first re- 

 folding occurs: the other flexures are indicated in Fig. 2. 



There is no line of demarcation between oesophagus and 

 stomach unless, as stated by Balfour and Parker (3), " a glan- 

 dular posterior region be regarded as the stomach, a non-glan- 

 dular anterior region forming the oesophagus." The macro- 

 scopic appearance of this region gives no indication of the 

 position of the boundary line between the two parts. The 

 intestine is of about the same size in all parts. The pyloric 

 caeca are so small and numerous that the caecal mass formed 

 by them presents an almost brush-like appearance. The caecal 

 cavity extends into the finest subdivisions of the gland. The 

 peritoneal coat is unpigmented. The short spiral valve makes 

 only two or two and one-half turns, and ends about two centi- 

 meters from the vent. In connection with this part of the 

 intestine is a structure referred to by Balfour and Parker as 

 follows: "The posterior part of the intestine, from the begin- 

 ning of the spiral valve to the anus, is connected with the ven- 

 tral wall of the abdomen by a mesentery. . . . This mesentery, 

 which together with the dorsal mesentery divides the caudal 

 section of the body into two lateral compartments, is, we be- 

 lieve, a persisting portion of the ventral mesentery which, as 

 pointed out by one of us,i is primitively present for the whole 

 length of the body-cavity. The persistence of such a large 

 section of it as that found in the adult Lepidosteus is, so far 

 as we know, quite exceptional. . . . The small vessel in it 

 appears to be the remnant of the subintestinal vein." My 

 specimen agrees perfectly with the above statement; the ven- 

 tral edge of the mesentery in this specimen measures at least 

 5 cm. in length. The blood-vessel, supported by the mesentery, 

 divides into two nearly equal branches, one of which extends 

 forward and the other backward, to be distributed to the ab- 

 dominal parietes. No reference to a ventral mesentery in any 

 of the other ganoids has been noticed, and the writer has not 

 had opportunity of examining other forms than Lepidosteus 

 and Amia. No ventral mesentery was found in Amia. 



The papillary structures found in the oesophagus of the 



1 Comparative Embryology, Vol. II. 



