THE STURGEONS AND STURGEON INDUSTRIES. 
243 
The figures of the young of A. ruthenm, the sterlet, given by Zograff, Figs. 19, 20, 
and 21, show that the dorsal scutes are developed before the lateral or ventral. This 
is also shown by the young of A. huso, figured by Brandt and Ratzeburg, but in not 
so marked a manner. The young of A. ruthemis, figured by Zograff, also shows that 
the scutes develop from before backwards. That is to say, there are as yet no fulcra 
shown on the dorsal margin of the tail, nor does the lateral series of scutes extend 
much beyond the vertical from the anterior end of the dorsal, as seen in Fig. 21. 
The tail is, in fact, fringed above and below only by fin-fibers or actiuotrichia, such 
as are usually the supports of the fins of young fishes. The narrow scutes or over- 
lapping fulcra of the dorsal margin of the tail are developed later, and derive their 
origin in the main from tissue elements which lie deeper than those which give origin 
to the actinotrichia and ultimately to the fin-rays proi^er of the adult. 
I am not inclined to agree entirely with Zograff as to the method in which the dor- 
sal scutes are developed, as given in No. 29, cited in the list of papers at the end of 
this monograph. In other fishes the actinotrichia or fin-fibers become embedded in 
the calcifiable matrix deposited around them, as my studies upon the development of 
the fin-rays of the salmon prove. That the scutes of the dorsal median line in stur- 
geons do develop partly at the expense of the embryonic fin-fibers is doubtless a fact, 
but that they are the sole basis of origin of the calcifiable matrix of the scutes in these 
forms does not seem probable, judging by what is known of the rays of other types. 
The so-called “fulcra"’ of the lower side of the caudal, at its anterior end, are not 
true fulcra, but ordinary fin-rays much modified. The same remark applies to the 
anterior elements of the dorsal. They are best developed in the adult in which they 
are much obscured by the increased thickness of the integument in the fully developed 
animal. 
4. THE ORGANS OF LOCOMOTION. 
The principal organs of locomotion are not the pectoral and ventral fins of the 
sturgeon, as might be inferred upon superficial inspection, bnt rather the powerful 
heterocercal tail, together with the dorsal and anal fins. The paired fins are subor- 
dinated in the main to the business of maintaining the equilibrium of the animal, that 
is, to keeping the dorsal aspect directed upward, and the ventral aspect turned in the 
opposite direction. 
The quite .young sturgeon, as shown by the appended Figs. 13, 14, 16, and 18, has 
a continuons dorsal and anal fin-fold the same as larval Teleosts. In other words, 
the sturgeon passes through a protocercal stage, as it was termed by Wyman, or a 
lophocercal condition, as the same stage has been called by the writer. Later, this 
continuous fin-fold finds support from within by the development of a continuous 
series of what have been inaptly called horn fibers, and which the writer has named 
actinotrichia. A large part of this continuous fold is absorbed and fails to develop, 
and only three portions persist and undergo further differentiation and growth as the 
dorsal, anal, and caudal fins. 
The dermal rays which are most obvious and easily counted in the dorsal, number 
from forty to forty-four in the adult sturgeon, and are about the same in number in 
the young of 7 inches in length. These rays are derived, in part at least, from the 
actinotrichia mentioned above. They support only the outer thin portion of the fin. 
