494 The American Naturalist. [May, 
The separation into two sets of fibres can be readily seen in the 
manner of grouping of the mesoderm cells, The exact manner in 
which muscle fibres arose from mesoderm cells, I was, however, unable 
to determine from my specimens. site 
Neither semen canal nor cartilaginous ‘‘ teeth ” had been found in the 
latest of my black-snake embryos, but both were present in the garter 
snakes. From this I infer that they arise at about the same time, and 
at about the same stage in the development of the organs. The 
semen canal is lined with large cells, continuous with those of the 
stratum mucosum, and is undoubtedly formed by an invagination of 
the epidermis. The ‘‘ teeth ’’ are modifications of the connective tissue 
walls, as Neumann has shown, but the exact manner of this change I 
could not determine. 
Lying behind the cloaca in the adult snake are two cone-shaped 
glands, with ducts opening to the exterior just behind the cloacal 
opening. : These are the “‘ anal sacs,” and secrete a stickly fluid, with 
a highly unpleasant odor. Rathke thinks this odorous fluid enables 
the sexes to find one another during the breeding season. 
These glands occupy, in the female, a corresponding position to 
that of the drawn-in penis in the male. Hoffmann® quotes Retzius 
to the effect that they occur only in the female, and are homologous 
with the male penis. Neumann finds them, though much aborted, in 
the adult male. In embryos I find them present, and of equal size in 
both sexes. They cannot, therefore, be considered homologues of the 
penis. Their ducts open to the exterior in the male, —not, as Rathke 
states, on the żzner side of each penis, but on the outer side. In the 
female they open in corresponding positions. 
These glands first appear in the embryos of the seventh week. 
Rathke’s statement that they arise as invaginations of the posterior 
wall of the cloaca does not agree with my observations. In my 
specimens they were formed by an invagination of the outer wall of 
the body just above the penis (Figs. 3, 4, s). The gland is formed, 
as Rathke states, by a continued growth inward of this invagination- 
Both. layers of the epidermis are carried in with it, and enter = the 
composition of the sac. In the ‘‘ grosszelligen ‘Plattenepithel, which 
rms its outer coating, Neumann recognizes a transformed stratum 
mucosum, now exercising a glandular function ; in a thin layer eor? 
ing its inner surface he finds the remnants of the original stra 
corneum.—AARON L. TREADWELL, Biological Laboratory of Wesleya 
University, Feb. 6th, 1891. i 
ê Bronn’s Thier Reichs, p. 1557. 
