262 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the head of young sturgeons up to 2 or even 3 feet in length, where the inner edges of 
these dermal bones have not yet developed a complete junction. 
The vertebral colnmn of the sturgeon consists of a notochord almost completely 
surrounded by rings of cartilage, the latter of which answer to the bony disks found 
in the vertebral columns of other types. Unlike all other types, except Branchios- 
toma, the lampreys, and a few Ganoids, and Dipnoans, the notochord of the stur- 
geon continues to grow uniformly in length and thickness thronghout life, and does 
not grow between the vetebral bodies only, as happens in the great majority of fishes^, 
nor does it even undergo partial suppression within a thickened outer sheath, as hap- 
pens in the Chimaeroids. 
The paired fins are snpported on cartilaginous basal pieces. The form of these 
pieces is well shown in Fig. 49, representing in stippled work the cartilaginous sup- 
ports of the rays of the ventral fin of the blunt-nosed sturgeon. The curious asym- 
metry of the segments of the basal pieces in this figure is worthy of notice. It is 
obvious that the three pieces of which the basal plate of either side is composed are 
greatly unlike. 
The further changes in the form of the head particularly, from youth to adult age, 
in the sturgeon, can best be realized by reference to the illustrations of the young of 
the common as contrasted with that of the blunt-nosed species on the three plates, XLV 
to XL VII, inclusive, and these compared in turn with the heads of an adult male and 
two females seen in three different positions, as shown in Plates XL VIII to L. 
These figures are the first adequate pictorial representations of these fishes which 
have been published, and since they have been obtained with the help of the photo- 
graphic camera, from fresh materials, they can be depended upon as being accurate. 
The proportionally narrower head of the adult male is well shown on Plates XLVIII and 
L, while the great dififereuce in the width of the mouth of the young of A. sturio and 
A. brevirostris is strikingly displayed on Plate XLVIL The first loop of the intestine 
exposed in the young of the common sturgeon, and represented on Plate XLVII, is seen 
to extend proportionally much farther back than in the adult, shown with the viscera 
exposed, in Plate LI, where this portion of the intestine is the only part of the ali- 
mentary tract which is uncovered. The metamorphosis of the sturgeon, according to 
the data given in this brief sketch, is seen to extend over a prolonged period, and to 
involve not only the fins and integumentary plates but even the relative proportions 
of the viscera. 
9. THE SOURCES OF THE FOOD OF THE STURGEON. 
When the young of the common sturgeon is first hatched it measures barely half 
an inch in length. At this time there is still present a quite large yolk-sack filled 
with a yellow opaque yolk subtance, the sides and upper surface of which are shaded 
with brown, owing to the presence of fine granules of pigment embedded in its super- 
ficial stratum. After a few days this yolk material is absorbed and the young fish, 
now measuring nearly three fourths of an iuch,^ must begin to forage for itself. As 
•The embryos of Acipenser sturio are considerably larger than those of A. ruthenus as measured by 
Salensky and Balfour. This difference is doubtless due to the difference in the size of the ova of the two 
species, the eggs of the common sturgeon being more than half a millimeter larger in diameter than 
those of the sterlet. The former measure 2.6“'“, while the latter measures only 2“”" in diameter. The 
larval sterlet, furthermore at the time of hatching, measures only while the larva of the common 
American species at the same stage measures 11™™. 
