370 Dr. Wyman on the Surinam Toad. 
fourteen. The structure of the sac may be understood from an 
inspection of fig. 1, which represents a magnified vertical sec- 
tion through the whole thickness of the skin: a@ represents the 
operculum, 6 the epidermis, ec dermis or true skin, aud d the 
yelk with its embryo. The sacs are at variable distances from 
each other, sometimes so closely approximated that the interven- 
ing integument is reduced to the thickness of a piece of paper. 
The operculum adheres to the circumference of the mouth, and 
there is usually found just beneath it a layer of gelatinous matter 
which is continuous, in some instances at least, around the whole 
circuinference of the egg. The structure of the operculum as 
seen beneath the microscope was not homogeneous, but seemed 
to be composed of ill-defined fibres, not unlike those of the white 
element of areolar tissue, and there were intermixed with them 
granules of pigment. The interior of the pouch was covered by 
a layer of pavement epithelium, continuous at the orifice with the 
cuticle covering the surface of the body; it was easily detached, 
and its cells were nucleated and contained colored granules. Be- 
neath the skin there exists over the whole back a large cavity, as 
in Frogs, but unlike the one in them no nerves were seen pass- 
ing through it, in the region of the spine, to the integuments. 
‘he eggs are quite remarkable when compared with those of 
other Batrachians for their great size, the yelk alone measuring 
oue-fourth of an inch in diameter. In almost every instance, 00 
removing the operculum, the embryo, however small, was ound 
just beneath it, and thus occupying a position on the yelk which 
had the nearest proximity to the air. 
In the earlier stages, as seen in fig. 2, the head is broad and 
flat, the cerebral vesicles are easily detected, the lateral portions 
not having united on the median line; the eyes were prominent 
i 2. 3. 
portion of the trank, but the legs consisted of oval masses entirel 
disconnected with the parts surrounding the vertebral colum®, 
and seemed to have an independent centre of growth, aud 
earlier spect 
t 
did not bud out from the trunk. In all of. 
