720 THE AMERICAN NATURALIST. [VoL. XXXIV. 
rather square meshes than was the case cephalad. Their free 
edges also seem to be less jagged, but, like those cephalad, 
they have wavy, free edges, and between the higher convolu- 
tions there are lower ones somewhat connected with the larger 
ones or free. There are comparatively few large, free projec- 
tions or villi in this region. 
At the beginning of the second turn the regular network 
appearance is usually lost, and the projections shorter, more 
irregular, and more jagged. After the most cephalic face of 
the spiral valve is passed, there are a few long, straight folds 
which appear to run in a longitudinal direction when the intes- 
tine is cut open lengthwise and slightly distended. Most of 
the other folds of the spiral valve might almost be considered 
to be villi, with rather broad bases and sharp tips. Below the 
spiral valve the convolutions are usually almost all longitudi- 
nally disposed; there are quite a number of low projections 
nearly free from each other, having rounded edges and ar- 
ranged' in parallel lines, almost like villi, but usually joined 
to each other by their bases. 
The above description applies especially to medium-sized or 
rather large specimens, many points being obscure in smaller 
individuals, partly because of the smaller size of the convolu- 
tions, and partly because of individual variations. Aside from 
the usual variations which occur in all specimens without any 
special rule, there is a way in which large specimens differ from 
small in quite a constant manner ; that is, the difference in the 
height of the convolutions, the larger individuals usually having 
longer projections than the smaller. This difference is rather 
a general one with the villi of many mammals and birds. 
The muscular coats of the intestine are, as in all vertebrates, 
an outer longitudinal and an inner circular. The longitudinal 
coat is rather thin and made up of small, more or less irregular, 
bundles of plain muscle. The circular layer of muscle is enor- 
mously developed and, for most of its extent, seems to be of 
about the same thickness. There is but scant connective tissue 
about the bundles which make up the inner coat, while the 
connective tissue about the smaller bundles of the longitudinal 
coat is well developed. These muscular coats vary but little 
