202 General Notes. | February, 
out the entire extent of those folds; Alosa, also a physostomous 
form, does not have them developed nearly so extensively at a 
corresponding period. In forms with discontinuous folds, as 
Siphostoma, for example, they are not very evident even at the 
time when the caudal rays are being formed, but aside from such 
exceptional forms they seem to be almost universally developed to 
some extent in the fin-folds of all truly fish-like forms except the 
lampreys and the lancelet. 
In consequence of the striking resemblance which this stage of 
the development of the rays of the most specialized fishes bears 
to what has remained nearly permanent, with but comparatively 
little modification in the Chimzroids, Elasmobranchs, Ceratodus 
and Protopterus, I propose to call this the protoprerygian stage of 
the development of the fin rays in the Teleostei. The primitive 
fibers in section are shown to be perfectly cylindrical and homo- 
geneous, and so far as histological tests enable me to judge, are 
perfectly similar in composition to the homogeneous semitubular 
matrix derived from the former, in which ossification occurs to 
form the permanent rays. Active metabolism evidently occurs 
at the base of the fin-folds about the time the permanent rays are 
in process of development, for the reason that after the stratum 
of fibers becomes covered externally by mesoblast in this situation 
they rapidly atrophy leaving nothing but the semitubular rudi- 
ments of the permanent rays, crescentic in section, which now 
lie between the epiblast and mesoblast resting upon thickened 
tracts of the latter internally and which radiate toward the mar- 
gin of the permanent caudal fin-fold ; the proximal ends of these 
mesoblastic cores rest upon the distal end of the upturned 
chorda. 
The segmentation of the permanent rays has not been traced, 
but this evidently occurs before ossification has gone very far, as 
it is manifested quite early in the caudal rays of certain types. It 
.is doubtless due in part to the bendings which the rays suffer 
while in use. The rudiments of these rays are imperfectly tubu- 
lar in all forms, spines also having such a form at first, thoug 
frequently these have an external layer added by coalescence 
with dermal plates or denticles. 
The main conclusion, therefore, at which I have arrived in this 
investigation is the following : that it is the mesoblast which is 
involved in giving origin to the fibrous embryonic rays and that 
that layer also effects their transformation into the rudiments ot 
the permanent rays, and not the epiderm or embryonic integu- 
ment, as heretofore generally held by anatomists. The whole 
history of the fin-folds in fact favors such a conclusion, since the 
horny fibers develop between the corium and epidermis or em- 
bryonic skin, in the plane of the protomorphic line of Huxley. 
The fin-folds of embryo fishes, it should be borne in mind also, 
are at first wholly epidermic, the corium or true skin being only 
developed during the later-larval or post-larval life. 
Be SS n TE. POP ireae 
SO Em ie NO A E A S Oe ee a a ee ee ey ee | 
De ae een gee re ON yl S ay A ca a ne Ne Sane I ESET ag 
