NOTES ON THE DEVELOPMENT OF THE NEWT. 583 
some cases situated one above each gill-cleft. At the same 
time he is obliged to assume the existence of more than one 
now aborted gill-cleft, in order to account for the number of 
the sense-organs. If the proof of the segmental value of the 
sense organs is to depend on the number of the gill-clefts, and 
the number of the gill-clefts is in turn to depend on the 
segmental value of the sense organs, it is difficult to discern 
which is the basis of the argument. Malbranc (15) shows that 
even in the embryo multiplication of the sense organs by 
division may occur, so that the number of them seems to be 
indefinitely variable ; and Mr. Beard himself has described such 
a division in the case of the sense organs of the facial nerve. 
It seems, therefore, that there was primitively only one such 
sense organ in this case, and that one cannot depend on the 
number of the sense organs at any but the very earliest stages, 
if even then, as indicating segmentation. 
SuMMARY OF OBSERVATIONS. 
1. Asolid post-anal gut is formed behind the blastopore (anus), 
growing out into the tail, and fusing with the undifferentiated 
tissues at its posterior end. The fusion of hypoblast and 
epiblast in this region represents the neurenteric canal. 
2. In the Frog the post-anal gut is at first hollow, but after- 
wards becomes solid. 
3. The stomodeum and pituitary body are derived from a 
solid ingrowth of the inner layer of the epiblast. The hind 
part of this ingrowth fuses with the front wall of the fore-gut, 
but the perforation to form the actual mouth does not appear 
till after hatching. The pituitary body grows upwards as a 
solid cord, and applies itself to the infundibulum in the ordinary 
manner. 
4. From the hind border of the stomodzeum proceeds a solid 
rod of cells, which constitutes the thyroid body, and is de- 
veloped from the cells of the middle ventral line of the fore- 
gut. 
5. The development of the peripheral nervous system is 
