244 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the rays of which are jointed at close intervals in the adult, but iu the young the 
joints in the individual rays are fewer. 
The dermal rays of the dorsal are supported at their lower ends upon about thirteen 
cartilaginous neural bars or processes which do not in turn rest in immediate contact 
by their lower ends upon the neural arches. The lower ends of the series of carti- 
laginous rods which support the dorsal flu extend over about five neural arches with 
their intercalary pieces. 
The twenty-six to thirty dermal rays of the anal fin are supported on about ten 
cartilaginous haemal processes, and these in turn are supported proximally by about 
four pairs of cartilaginous haemal arches and intercalary pieces. 
In the lower lobe of the caudal, that is, below the posterior iiart of the notochord, 
to its termination, in the caudal fin, there are about ninety dermal rays in the com- 
mon species. These are supported on about twenty-five cartilaginous haemal proc- 
esses, which diminish in size toward the end of the tail so as to appear as if totally 
degenerate toward the last of the series. On the dorsal side of the caudal a series of 
fulcra are developed; these are merely a continuation of the more anterior series of 
median dorsal plates the development of which has been modified. The reason for 
this conclusion is the fact that, as Zograif has shown, in A. ruthenus, the dorsal series 
of scutes develop in the median fin-fold, which involves actinotrichia embedded in the 
membranous portions of the fold which intervene between the sharp tips of the scutes. 
The latter also iu the earlier post-larval stages overlap much as do the scutes known 
as “fulcra” along the dorsal margin of the tail. These facts are of the greatest pos- 
sible significance as giving us a more comprehensive view of the origin of the 
so-called fulcra of ganoid forms. This much is at least assured, viz, that the method 
of evolution of the fulcra in all ganoids will be found to be essentially the same. That 
the deduction reached above is true is further fortified by the fact that in young stur- 
geons 7 inches long there are present true primitive fin-fibers or actinotrichia behind 
the last formed fulcra and inclosed within the persistent continuation of the median 
dorsal fin-fold over the tip of the tail. Actinotrichia or primitive fin-rays are certainly 
involved iu this process, to which other calcifiable matter is doubtless added in the 
later development of scutes aud fulcra. The phylogeuy of the fulcra as displayed by 
the sturgeon, by Chondrosteus and Grossopholis, the extinct sturgeons, is significant of 
how such consecutive modifications arose in other forms. 
The further conclusion which is of some importance from a morphological stand- 
point, is the fact that the main parts of the fulcra are not wholly comparable with true 
fin-rays, but are derived from the cells of a deeper portion of the corium, which, as in 
the case of the large lateral, ventral, and dorsal scutes, involves the very deepest layers 
of the integument. Few or no true primitive fin-rays therefore persist along the dor- 
sal margin of the tail, except at its extreme posterior extremity. The inferior side of 
the caudal fin may therefore be said to be the only portion which supports true “soft” 
rays. The expressions “upper” and “lower lobe” are therefore simply names for 
parts of the caudal which stand in dorsal and haemal relation to each other, and have 
no real morphological significance, for even the rays of the upper aud Ipwer lobes of 
the caudal of symmetrically homocercal forms are really ventral to th'J primitive cau- 
dal axis or notochord. In the adult sturgeon this arrangement clearly persists in a 
comparatively embryonic form, with all of the true fin-rays iu a ventral position. 
