THE STURGEONS AND STURGEON INDUSTRIES. 
261 
The next changes which are of interest in the progress of the metamorphosis of 
the sturgeons have been illustrated by N. Zograff, whose figures of the young sterlet 
I have not hesitated to lay under contribution. In these the snout is seen to have 
become distinctly more pointed and flattened underneath, as shown in Figs. 19, 20, 
and 21. The barbels have been lengthened, but seem to radiate from a central point, 
as shown in Fig. 20, from below. 
The greatest interest, however, attaches to the history of the median dorsal row 
of scutes or bucklers. These seem to arise within the partially suppressed median 
dorsal fin-fold and, as shown in Fig. 26 (considerably enlarged), their points are very 
sharp and overlap somewhat in the same way as do the fulcra or plates on the dorsal 
margin of the tail in the adult. The dorsal bucklers appear first and before the fulcra. 
The lateral plates appear at the same time as a row of smaller calcifications in the 
integument of the sides, the anterior plates being the largest. The ventral rows of 
bucklers seem to be wanting, but they evidently appear, in some species at least, very 
soon after this stage has been passed over. This conclusion is supported by the con- 
dition of an older stage of another species, A. huso, represented of the natural size, in 
Fig. 22. In this figure all the bucklers seem to be present, except the fulcra of the 
dorsal margin of the caudal fin. The form of. the head and snout also presents very 
nearly that which is so marked- in the young of all the species, namely, the great 
elongation, flattening, and narrowing of the portion in advance of the eyes. 
In Fig. 17 it is seen that fine cartilaginous branchial arches are developed in the 
larvae behind the hyomandibular bar, which indirectly helps to support both the 
lower jaw in part and the hyoid arch wholly. The arrangement of these parts is still 
more clearly shown in Fig. 44, illustrating the cartilaginous cranium of the adult. 
Though there are five gill-bearing arches developed, it is only the four anterior ones 
which support true gills; the hindmost or fifth is reduced in length and is completely 
embedded jn the tissues at the posterior end of the branchial chamber, and bears no 
branchiae even in the adult. 
The figures of the young larvae and post-larval stages show that the head is at first 
without armor-plates or scutes; in other words, it is covered by the naked integument 
only during the early life of the animal. In the young fishes from 4 to 5 inches long 
the cranial plates are already formed ; their arrangement over the top of the head is 
essentially that displayed in Fig. 45, for all the species, barring minor variations. The 
most constant plates are the supraoccipital, exoccipital, parietals, and frontals. These 
form, together with smaller plates over the top and sides of the snout, a complete 
bony investment for the cartilaginous skull or brain-box shown separately in Fig. 44. 
The armor is completed at the sides by the large single opercular plate and below by the 
parasphenoid. All, or nearly all of this bony investment of the skull, except the pos- 
terior portion of the parasphenoid bone, is developed from calcifications which start 
from separate centers in the skin, so that all of these superficial bones of the head are 
regarded together with those on the back, sides, and under sides of the body as dermal 
or integumentary bones. They grow in extent by adding more bony substance to 
their edges, so that their roughly-indented edges ultimately fit together at their edges 
so as to form a more or less close anion by the method which is known to anatomists 
under the term sutural. As pointed out elsewhere, the last pair of plates to unite and 
thus completely cover in the cartilaginous cranium in the common sturgeon are the 
parietal and frontal pairs, so that a fontanelle or hole may be detected in the top of 
