151 
STUiiGEONS. 
Ills journey into Siberia, mentions an example, of only six 
feet long, tlie roe of wliich measured tiro quarts j and another 
is recorded, that weighed two hundred and seventy-three 
pounds, the roe of which amounted to forty-two pounds, the 
supposed number being almost two millions. It is not there- 
fore in purses, or by internal hatching, that the young are 
produced to life, but more strictly in the manner of bony 
fishes, the grains being, however, rather large, and separated 
from each other throughout the mass by layers of fat. It is 
one of the principal objects of the Eussian fisheries to obtain 
this roe, which is carefully prepared, and valued by epicures 
under the name of Caviare. 
Another valuable product of this fishery, and of more general 
importance, is isinglass; which is formed of the air-bladders 
of two or three species of tliis genus, and of which, one of 
the smaller kinds, ( A. ruthenus,) is said to produce the best. 
The organ from which it is prepared is not found in any other 
of the plagiostomous genera, Shai-ks or Skates ; but in the family 
of Sturgeons it appears to be of great use in enabling the 
fish to rise and fall frequently and rapidly amid the currents 
of the larger rivers, as well as in the deeper waters of the 
sea. The stnicture of this organ has remarkable peculiarity, 
in the existence of a duct or passage of no small size, which 
passes from the bag to the gullet, and by which the air within 
may be occasionally discharged, and perhaps again renewed 
from without; for we are not able to affirm positively what is 
the special or complicated object of a structure which is only 
shared by a few of the fishes furnished with an air-bladder. 
In an example of the Common Sturgeon, of about eight feet 
in length, which I knew caught in a trammel in the open 
sea, as the fish was raised from the ground some observable 
bubbles of air were seen to break from the water; and I 
have no doubt they had been discharged from the fish, perhaps 
under the influence of the terror produced by its capture. 
Isinglass was known in ancient times by the name of 
ichthyocolla, or fish-glue, and it was used in the medical 
practice of Greece and Eome as a principal ingredient of 
their adliesive plaisters; but the fishes which produced it 
were on another account a subject of attention to the Eomans 
of the flourishing times of the emphe. 
