THE STUEGEONS AND STURGEON INDUSTRIES. 
263 
the oral opening is very small at this time it is necessary that the food taken be quite 
small. The mouth now becomes transverse and ventral in position, more or less pro- 
trusible as in the adult, and up to the third month the jaws support microscopic teeth 
of a very simple, conical type. The food taken at this time must be microscopic in 
character, and probably consists of rhizopods, unicellular algae, infusoria, minute 
larvae of insects and worms, crustaceans, etc., so that the range of forms upon which 
the life of the young sturgeon depends during its early stages of growth is a very wide 
one. The rhizopods, algae, and infusoria are probably skimmed from the surface of 
the ooze at the bottom of the estuaries where the young sturgeon must feed during 
the early part of its life. That the young sturgeon does feed upon I'hizopods to a large 
extent is to be inferred from the similar habit of the young of the Catostomidce or suck- 
ers as first determined by Prof. S. A. Forbes. In slides prepared by Professor Forbes 
from the intestinal contents of a species of Myxostoma and one of Erimyzon (Proc. 
Acad. Nat. Sci., Philad’a, 1881), Professor Leidy was able to distinguish the shells of 
six distinct species of rhizopods or test-covered protozoa. The habits of the young 
sturgeon must be similar, for a time, to those of the Catostomidce on account of the 
similarity of the mouth of both, so that, infereutially at least, there is strong proba- 
bility that amcehoid protozoa at first constitute an important part of its dietary. 
It is thus rendered at least highly probable that there is an interdependence of 
the one upon the other in the struggle for existence. And one may legitimately 
speculate as to the still lower origin of the food of the protozoa. 
The latter take> into vacuoles or spaces in their sarcode minute vegetable and 
animal organisms which are digested and incorporated into their own substance, 
which is thus made to grow in amount. The rhizopods, in turn, are swallowed by the 
larval sturgeon, and we thus perceive that the minute accumulations of organic mat- 
ter' represen ted by the lowest protozoa are finally incorporated and become an integral 
part of a still larger aggregation of organic matter with a much higher grade of organ- 
ization. The first process of digestion and integration took place in a mere cavity in 
the protoplasm of the very lowest grade of organization ; the next step in the process 
of digestion and integration of living matter took place in a higher type in a differen- 
tiated alimentary tract with cellular walls and special glandular appendages which 
furnish the special food solvents or digestive ferments. 
After the young sturgeon becomes somewhat older, larger forms are preyed upon. 
By the time the young animal has reached an inch to an inch and a half in length, 
the dorsal and lateral plates begin to appear, and the cartilages of the head and ver- 
tebral column have been formed, but the ribs are not yet developed, according to the 
sections figured by Zograff. Minute teeth are present on the pharyngeal floor and 
the food may be identified in the sections through the region of the stomach and 
intestine. The most characteristic and abundant of the intestinal contents at this 
time are the tests and remains of the soft parts of Cladocera or Daphnidw, small water 
fieas, the summer broods of which are parthenogeuetic and multiply at a prodigious 
rate, so as to be very abundant in the fresh-water estuaries where the young stur- 
geons are numerous. The figures of sections given by Zograff of the young of the 
sterlet, display the stomach and intestine literally packed with ihe remains of Daph- 
nidw, so that it is obvious that during some portion of the sturgeon’s life and under 
certain conditions these forms stand in a vital relation to the latter as its food. 
Doubtless other forms, such as algae, minute fresh- water worms, fish larvae, insects and 
