726 THE AMERICAN NATURALIST. [Vor. XXXIV, 
species a long time for specialization, so the intestine has, 
during at least part of this time, become highly specialized, 
probably to suit more exactly the character of its food. 
Another interesting point about Amia is the fact that in the 
spiral valve there is more muscular tissue than could have been 
derived from the muscularis mucosa. How did it get there? 
The answer to this question can be solved definitely only from 
the standpoint of embryology, but perhaps a suggestion may 
not be out of place. If the spiral valve was originally, if not 
in Amia in its progenitors, formed by a twisting of the whole 
thickness of the intestine, then a folding of the whole wall 
would, of course, involve the muscular coats as well as the 
submucosa and mucosa. In such a case muscle would be left in 
the spiral valve after readjustment of the outside coats once 
more to their usual appearance. Muscle from the muscularis 
mucosa would also be in the spiral valve, but the greater part 
would be from the muscular coats, and, because of the thick- 
ness of the inner muscular coat, the larger part of the muscle 
would run transversely, as is actually the case in the spiral 
valve of the adult. | 
GENERAL CONCLUSIONS. 
I. The intestinal convolutions are very complex in form and 
arrangement, being made up of variously shaped folds and free 
projections or villi. 
2. The muscular coats are well developed, an outer longitu- 
dinal and inner circular, the latter very thick. 
3. Athick connective-tissue band, of uniform nature through- 
out the intestine, occurs next the inner muscular coat. This 
band of connective tissue sends up projections of fibres into 
some folds and villi. 
4. A muscularis mucosa is present, a few fibres of which are 
prolonged into the cores of folds and villi. 
5. The epithelium is simple, columnar, four to eight layers 
of nuclei appearing in sections. 
6. The epithelium is not ciliated, except for a small area 
caudad of the spiral valve. 
