526 JULIA B. PLATT. 
At each side of a mid-dorsal fold in the skin a row of mucous 
glands is found, composed of a few cells invaginated from the 
deeper layer of the ectoderm, and now lying below the surface, 
tiny balls of cells surrounding a central cavity that opens to 
the surface by a small pore. Similar glands are found on the 
ventral surface of the body between the fore-limbs, and on the 
tail. Although these glands are about the size of sense-organs, 
nothing in their structure or in the manner of their develop- 
ment suggests that genetic relation of sense-organ and mucous 
gland on which Leydig (26) insists. 
Pl. 38, fig. 33, represents the ventro-lateral surface of the 
head, showing the position of the anterior sense-organs and 
the distribution of pigment, which, as the figure demonstrates, 
makes the position of the dorsal sense-organs less apparent. 
I have omitted the pigment in fig. 32, which shows the dorsal 
sense-organs of the head and the sense-organs of the three trunk 
lines. The pigment cells are so grouped that a light band with 
irregular outline extends on each side of the embryo throughout 
the length of the body. Its position and relative width are 
shown in the small area over which, in fig. 32, the pigmenta- 
tion is reproduced. The anterior sense-organs are also out- 
lined in fig. 31, which gives their innervation. 
Comparing the sensory differentiations of the ectoderm at 
this stage with those of the younger embryo represented in 
fig. 21, one finds that a cluster of sense-organs has developed 
on the antero-ventral surface of the snout at the anterior 
extremity of the supra-orbital line. The two groups on oppo- 
site sides of the head lie near to one another, but do not meet. 
At the anterior extremity of the infra-orbital line a similar 
cluster of sense-organs is found, resulting from the continued 
multiplication of sense-organs between the eye and nose, which 
had already begun in the younger embryo. The organs at 
the posterior extremity of the supra-orbital line have extended 
in a postero-dorsal direction beyond the point where this line 
meets the infra-orbital, and the angle at which the two lines 
diverge is now more acute. 
The change in the relative position of the hyomandibular 
