718 THE AMERICAN NATURALIST.  [VoL. XXXIV. 
the abdominal cavity. After the first turn the intestine is of 
considerably less diameter than that of the first part. This 
second part, after quite an acute angle with the first part, as- 
cends parallel with it for from one-third to one-half of its length, 
and then, after a very sharp turn, descends once more. After 
a few centimeters of descent the intestine bulges out to a large 
diameter, indicating the location of the spiral valve; as it ap- 
proaches the vent, the spiral valve having ended, the intestine 
once more becomes of small diameter. The spiral valve, which 
occupies a few centimeters of extent above the end of the rec- 
tum, has from four to four and one-half turns (Hopkins, '95). ° 
Before taking up the finer structure of the intestine, the 
general form and arrangement of the mucosal convolutions will 
be considered. In this part of the study it was found that the 
character of the convolutions was much more easily and accu- 
rately made out from gross’ preparations than from sections, 
for, although serial sections may show much, a clear compre- 
hension of all the complications can be obtained only by ex- 
amination of the whole ental surface of the intestine. The 
following description is largely taken from a single specimen, 
one having been selected in which the most characteristic con- 
dition was presented. Upon a superficial examination of the 
intestine, slightly distended, the whole ental surface appears 
to be covered with villi thickly and irregularly placed, varying 
somewhat in height, but less in general shape, at different parts 
of the intestine. These appearances are to some extent decep- 
tive; the upper part of the intestine is covered with a network 
of long and short zigzag folds and isolated vill. The folds run 
in every direction, and their free edges are more or less irregu- 
larly but deeply notched or wavy. Some of the projections or 
villi are perfectly isolated; others, which at first sight seem 
to be perfectly free, are found on more careful examination to 
have connection with their neighbors at the bases. There 
are all gradations, from perfectly isolated , villi to irregular, 
short, zigzag folds. Many folds or nearly perfect villi join egch 
other throughout their whole height; others slightly at their 
bases. All are of irregular, undulating heights. Many folds 
are several centimeters in extent, so that a very complicated 
