694 THE AMERICAN NATURALIST.  [Vor. XXXIV. 
The dorsal skin of the female thickens about the eggs, until 
each is enclosed in a dermal “ cell" or sac, which is finally 
covered by an “operculum.” Leydig (96) regards the cells as 
modified glands, and, in corroboration of his view, states that 
other dermal glands are not found where the cells are formed; 
he regards the cap of the cell as a secretion of the gland, while 
formerly it was thought to be a hardened portion of the gelat- 
inous substance around the egg. Whatever the origin of the 
cells, they are temporary structures which form in response to 
the stimulus of the eggs; the number of eggs carried by one 
frog has been variously estimated, and may be more than one 
hundred. 
The eggs develop entirely within the dermal cells, and Fer- 
min has observed that they remain about eighty-two days on 
the back of the parent. I have found no direct statement as 
to whether the time of hatching is coincident with the time of 
leaving the dermal sac, except in Bronn's Thierreich. There 
it is said that *the hatched young find shelter and nourish- 
ment on the parent's back, until after completed metamor- 
phosis," implying that the eggs are hatched some time before 
the young escape. 
The only description of development, based on the observa- 
tion of many embryos, is one by Jeffries Wyman (54), giving 
the external characters of three stages. 
The limbs develop early ; even in the youngest stage, where 
there were three pairs of external gills, the fore and hind legs 
were present, in the condition of knobs at the sides of the 
embryo, the posterior said to be unconnected with the trunk. 
There were at this stage vitelline vessels, supplying the large 
yolk-mass. The head was broad and flat, with conspicuous 
cerebral vesicles and prominent pigmented eyes; the spinal 
cord was closed. 
Later (in the second stage), when the external gills had 
disappeared, fringed branchial arches were seen by removing 
the dermal folds which concealed them ; the opercular folds 
opened by a small branchial fissure on each side of the neck, 
and judging from the figures, did not cover the anterior legs. 
Rudiments of feet were present on all the extremities. It 1s 
