628 . SKATES’ EGGS AND YCUNG. 
pea have found them when first formed, growing from the outer edge 
the branchial arch (figs. 89 and 90), and at that time in no way con- 
ind with the branchial fissures. In the skate, the first and seventh 
arch had no fringes at any period, and of the five which had them, the 
fringes of the foremost ones were the longest, the hindmost being merely 
short, conical projections. As development advances, the bases of the 
fringes are gradually covered up, as it seems, by the growth of the por- 
tion of each arch in front of them, which is itin projected outward as 
the body becomes thicker from side to side; the line of attachment of the 
fringe, which retains its origi- 
nal position, being thus buricd 
between two adjoining arches. 
From the fact that the tem- 
e porary gills are formed before 
the permanent ones, and from 
the outer surface of the arch, it 
s obvious that they cannot be 
—as commonly described—pro- 
longations of these last-meu- 
tioned breathing org 
The fringes do ues cover the 
whole border of the arch, but 
are confined tu its central por- 
tion, and consist of from six to 
eight filaments each. 
We have made no observa- 
tions on the formation of the 
internal gills, and cannot there- 
fore explain the connection 
which eventually exists be- 
tween these and the fringes 
sal and ventral views of fig. a, a’, pee and which at a later period 
Dor 
toral “fins; b, facial disk: c. ian Sy imd d, anal res ; cactly rj the 
fin; d', dorsal fins; e, gill fringes. correspond exactly with 
Fig. 94. 

descriptions usually given 
The existence of temporary branchial fringes, and their subsequent 
absorption, is one of the most remarkable characteristics of Selachians, 
and one in which they differ from all osseous fishes, unless it be the Lepi- 
dosiren. All vertebrates, as embryos, agree in this, that they are in their 
early stages provided with “branchial fissures” and “arches” or, as they 
sometimes have been called ‘visceral’ arches. Gills or gill fringes, either 
as temporary or permanent structures, are never formed in any scaly rep- 
tile, bird, or mammal. Much confusion and misapprehension have arisen 
from the constant reiteration of the opinion put forth in the early days of 
embryology, that all vertebrates at one time have a branchial cer 
an error which is repeated by naturalists even at the present day. Among 
Batrachians some genera, as Menobranchus, Siren, etc., have external 
