NOTES ON THE DEVELOPMENT OP THE NEWT. 243 



seen to occupy the normal position of the post-anal gut, being 

 situated between the dorsal aorta and caudal vein. 



In the Frog we find a post-anal gut with a wide lumen 

 behind the blastopore. The lumen gradually narrows towards 

 the hind end, and loses itself in the indiflferent tissues of the 

 tail. This stage is somewhat later than that recently described 

 by Mr. Durham (23), with a complete open neurenteric canal. 

 The canal must evidently be drawn out with the growth of the 

 tail, and two regions can then be distinguished in it, the post- 

 anal gut and the neurenteric canal proper. The lumen is 

 obliterated from behind forwards, the neurenteric canal becom- 

 ing closed first. This would account for the condition we find. 

 Later, the lumen of the post-anal gut is lost, and it becomes 

 a solid structure. 



Dr. Gasser gives an account of a post-anal gut in Alytes (8) 

 like that of the Newt. The lumen of the alimentary canal is 

 continued a very short way into it, and the rest forms a solid cord 

 in the tail. There is no open neurenteric canal in Alytes. 



A post-anal gut of the same kind has been described by Mr. 

 Shipley in Petromyzon (20) . 



The StomodjEUm and Pituitary Body. 



The stomodseum developes as a solid ingrowth of the inner 

 layer of the epiblast just in front of the anterior wall of the 

 fore-gut (fig. 12). The lower pai't of the ingrowth fuses with 

 the fore-gut (figs. 14, 8, 9) while the upper projects freely and 

 forms the pituitary body (fig. 14). In fig. 8, which represents 

 an oblique transverse section, the relations of the pituitary 

 body to the stomodseum and fore-gut may be clearly seen. It 

 grows upwards and applies itself closely to the infundibulum, 

 curling round it (fig. 14) and forming an indentation in its 

 floor (figs. 38, 37, 36). The extreme end of the pituitary body 

 is shown in fig. 38, where it is hardly distinguishable from the 

 infundibulum. 



The stomodseum fuses with the fore-gut at a very early 

 stage, but no actual perforation is formed until a short time 

 after hatching. The region of fusion takes on gradually the 



