SKATES' EGGS AND YOUNG. è 621 
velopment. has been thus far studied. As they grow, they advance on 
either side of the head in the form of horns (figs. 94 and 95, a’), but by 
degrees the space between these horns and the side of the head is filled 
up, and thus the eyes and the persistent portion of the first branchial 
fissure are pushed to the upper surface, and eventually the pectorals gain 
the foremost part of the side of the head, at the same time becoming 
united with the extended facial dis 
The tail, as the whole animal increases in size, becomes relatively very 
c Shorter. In the earlier stages the body is only three sixteenths of 
si entire length of the embryo, but subsequently it is about one half 
that length, as will be seen by a comparison of figs. 93, 94, 95, 96.” 
`“ Branchial Fissures and Gills. —1n nearly all adult Selachians there are 
five gill-openings in each side; Hexanchus and Heptanchus have respec 
tively six and seven such openings. In addition to these, all of the skates 
and some of the sharks have a peculiar opening just behind the eyes, or 
Fig. 93. 

More advanced embryo of Skate, having passed through the Eel and Shark- 
shaped stages and commencing to assume ind characteristic form of the 
ult. a, artery; 6, facial dis ski c, dorsal fins; anal fin. 
at some point between these and the first branchial fissure, which makes 
a direct communication, for the most part of a large-size, between the 
top of the head and the pharynx, and to which the terms ‘spiracle,’ 
‘event,’ ‘ Spritz-locher,’ ‘foramina temporalia, etc., have been applied. 
In the youngest embryos of skates here described, we have found the 
humber of gill-openings or branchial fissures seven on each side, all well 
defined except the last, which is the smallest of the series (figs. 88 and 
me These are all in the same range from before backward, and at this 
Stage the spiracle, as such, is not distinguished from the others. It is 
ae of the. early embryos of all Selachians, to have developed, 
in connection with branchial apparatus, temporary gills whieh are seen 
in the form of long and slender filaments projeeting from the sides of the 
neck. They are generally described as coming out through the gill- 
openings, and as prolongations of the internal gills. Cornalia, who has 
—— 
made a special study of these organs, so describes and figures them. We 
believe that, in consequence of not having seen embryos sufficiently 
young, he has been led into an error 
