248 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The economic use to which the air-bladder of the sturgeon is applied makes it 
of some interest to know how it is treated when it is intended to prepare fish glue, 
iehthyocolla or isinglass, as its gelatinous product is called, when isolated for com- 
mercial purposes. The air-bladders are removed and the peritoneal and connective 
tissue coverings carefully scraped off. The bladders are then dried and afterwards 
treated in a digesting apparatus to extract the gelatine which they contain. 
In the young sturgeon the course of the remainder of the intestinal tract is com- 
paratively simple, and it maintains the same arrangement in the adnlt, except that 
the proportional length of the duodenum, small intestine, and spiral valve are not the 
same. In the young the duodenum is proportionally longer than in the adult, and 
the same may be said of the small intestine. 
The duodenum extends from the pyloric valve or origin of the pyloric apparatus, 
backward and slightly to the left as far as a little beyond the beginning of the poste- 
rior third of the abdominal cavity, where it suddenly bends upon itself and passes 
forward to the right. This anteriorly deflected limb, or continuation of the duodenum, 
is the homologue of the small intestine of higher forms. It ends abruptly at the point 
where it passes into the hind-gut or spiral valve. The caliber of the spiral valve is 
somewhat greater than that of the small intestine and duodenum. 
The spiral valve is formed by a spiral fold which is developed along the walls of 
the hind -gut of the embryo. 
Beginning at the point where the small intestine bends upon itself abruptly to 
pass into the region of the spiral valve which takes a course straight backward, the 
spiral fold is seen to turn from left to right, or in the direction of the hands of a watch 
or dextral. The spiral fold makes seven complete turns or revolutions in the hind- 
gut, the last turn extending almost to the anus. In Lepidosteus there are but one and 
one half tuTus in the spiral valve, and it does not extend to the anus. In Ghimcera 
there are three turns in the rudimentary spiral valve; in the Dipnoans it becomes 
more developed, and in the Selachians reaches the maximum number of turns, though 
it would appear that the spiral valve in young embryos {Mustelus) have but three 
turns, while in the adult there are seven, so that at least four are added during the 
later development. This recapitulation by the embryo Selachian of the permanent 
condition found in Ghimcera is interesting as throwing some light upon the phylogeuy 
of the spiral valve. The function of the spiral valve is to increase the surface of the 
mucous membrane brought iu contact with the intestinal contents without lengthen- 
ing the intestine itself. 
The minute structure of the hind -gut or spiral valve is of considerable interest on 
account of the remarkable development of lymphoid tissue which is found along the 
edge of the spiral fold. In cross-sections of the intestine through the region of the 
spiral valve, the edge of the latter is found to be so greatly thickened as to form a 
cord like swelling along the whole extent of its free margin. When this thickened 
margin is examined microscopically it is found that its thickening is due to the pres- 
ence of a strand of lymphatic tissue, subdivided by partitions of fibrous tissue into 
nodules, so that it presents a strong resemblance to the structure of the lymphatic 
glands found in certain parts of the bodies of higher animals. The resemblance to 
the lymphoid nodules of Peyer’s patches in the walls of the ileum of higher forms is 
also suggested, and the presence of the largest lymph cells gorged with nutritive sub- 
stances along the surface of the glandular cord of the spiral valve of the sturgeon 
