246 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
any possibility of question were this the proper place to discuss the matter. At any 
rate, I now ijossess irrefragable evidence of the truth of the conclusion that some six I 
thousand species of living forms furnish a demonstration of Lamarck’s theory that the [j 
use of an organ may and does modify its structure, or that the actions of an animal 
react upon its structure, and modify the latter in the same way at every succeeding 
generation. Whether these modifications are inherited is immaterial, since the doc- 
trine of the direct effect of use and disuse is now demonstrable, and with all the rigor 
of method required in proving a proposition, in Euclid. 
5. THE VISCERA OF THE STURGEON. 
The abdominal viscera of the sturgeon embrace only, as here considered, the j 
alimentary canal and its appendages. The appendicular organs derived from the ali- 
mentary canal are the liver and gall-bladder, pyloric apparatus, and air-bladder. 
The organ mentioned by anatomists as pancreas in the sturgeon is not a diverticulum , 
of the intestine, but belongs to the series of ductless glands, and therefore represents I 
the milt or spleen, and is of mesoblastic, not of hypoblastic origin, as would be the I 
case were it a true pancreas. 
The alimentary canal proper is differentiated into three very clearly defined ■ I 
regions. 
The first of these is the oesophageal portion, and extends as far back as to the 
opening into the air-bladder. It is the narrowest portion, and leads directly out of the ’ 
branchial or pharyngeal region, beginning with the fifth and smallest and most poste 
rior of the five branchial arches. The branchial arches as they narrow by degrees 
from the first to the fifth form a kind of funnel-shaped framework which directs the 
food into the anterior end of the oesophagus or gullet. The gullet proper is then 
somewhat narrowed at a short distance from its anterior end, and upon being laid i 
open is found to be covered within tor some distance, with backwardly-directed, soft, j 
fleshy processes, into which its mucous membrane is elevated. At some distance, in 
its course farther back, its dining membranes again become smooth, but slightly j| 
folded longitudinally, and at a distance of an inch from its commencement, in a young | 
specimen 9 inches loug, it curves upon itself over to the left, and then forward and to ; 
the right, forming a loop, and beco mes more spacious. At the point mentioned it in ' 
fact widens into the stomach, which lies slightly to the right of the median line. The I 
stomach, especially at its pyloric end, is found to have very thick walls. This feature . 
is so strongly marked iu the adult that the organ acquires to a striking degree some j; 
of the characteristics of the muscular stomach or “gizzard” of a bird. This portion | 
of the stomach of the sturgeon is, iu fact, referred to by the fishermen in some local- ' I! 
ities as the “gizzard,” no doubt on account of this resemblance. | 
Immediately following the thick- walled stomach proper there occurs a very marked 
constriction of the alimentary canal. This constriction corresponds to the pylorus of ' 
Other vertebrates, and also marks the beginning of the duodenal portion of the ali- 
mentary canal, into the upper portion of which the pyloric apparatus or pancreas and 1 
liver discharge their secretions. 
Just behind the constricted pylorus proper a fold of the wall of the upper end of 
the duodenum is developed, which partly conceals the three wide openings into the ; 
pyloric apparatus or pancreas. 5 
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