KAYS. 
1093 
of work which he assigned on the one hand to the am- 
pulla? as secretory organs, on the other to the lateral 
line proper and the Savian vesicles as organs of sense, 
requires further demonstration. Its anatomical structure 
ranges the system of the lateral line with all its modi- 
fications as intermediate between the organs of hearing 
and those of the senses of pressure (touch — especially 
as in the worms), taste, and smell; and its physiological 
significance is perhaps best expressed as yet by Ley- 
dig’s assumption that it appertains to a sixth sense, 
foreign to us, arid receptive of the impressions yielded 
by such vibrations of the surrounding medium as are too 
grave (slow) for appreciation by the organs of hearing. 
The Rays probably spend the greater part of their 
existence in a stationary position at the bottom, and to 
facilitate their respiration, to keep the gill-slits supplied 
with fresh water, they have been provided with large 
spiracles on the upper side of the head, just behind the 
eyes. Above each spiracle is simple, below the passage 
divides into two, one branch entering the cavity of the 
mouth, the other passing to the gills. To prevent the 
water thus supplied from escaping through the mouth, 
they have a palatal fold, usually of powerful develop- 
ment, in the upper jaw. On the under surface of the 
head the nasal cavities show about the same relation 
to the mouth-cavity as in the Holocephali , only that no 
lateral upper lip encloses them outside and in front. 
Here the median upper lip instead is still more deve- 
loped, and forms a broad dermal fold extending from 
the anterior margins of the nostrils and between them 
back to the corners of the mouth a , on each side cover- 
ing a deep groove that runs from the nasal cavity to 
the corner of the mouth. On the outside this groove 
is bounded by a dermal ridge, which is indeed furnished 
anteriorly with a more or less prominent, blunt or 
rather pointed protuberance, but which does not form 
any limit between the anterior and posterior nostrils. 
The live pairs of branchial apertures are set on the 
ventral side 6 , in two more or less straight lines con- 
verging behind or in a curve anteriorly concave, pos- 
teriorly interrupted, behind the head and between the 
prorsal parts of the pectoral tins. 
As the form-series of the Rays, which includes 
about a hundred and fifty species, is a developmental 
offshoot of the Selachian type, the forms that have most 
widely diverged from the Sharks must, of course, be 
regarded as the most advanced in the scale of evolution. 
Among the Rays observed in Scandinavia there are two 
families which are both distinguished by the exceedingly 
slender (whip-like) tail and by the loss of at least one 
dorsal fin. In the third family of Scandinavian Rays 
both dorsal fins are persistent on the much broader and 
depressed tail, which is besides fringed on the sides 
with a more or less distinct dermal fold. But even 
this family is more widely removed from the Selachian 
type than the three remaining families, which are 
strangers to our fauna: the Torpedinidce , Bliinobcitidce , 
and Prist ides. 
Fam. M Y L I 0 B A T 1 1) M. 
The whip-like tail without caudal fin , hut with a dorsal fin in front , behind which there generally appears a 
serrated spine , with or without compensatory spine. The large pectoral fins interrupted on the sides of the head , 
hut continued on the sides of the snout by so-called cephalic fins. 
This family contains the giants among the Rays, 
some forms being veritable monsters of the deep. In 
addition to the characters given above the members of 
the family are distinguished by the elevation of the 
head above the plane of the pectoral fins, the forehead 
being especially high, and causing the eyes to assume 
a vertical position with lateral aspect, instead of the 
“ The above-mentioned intermediate forms (the Rhinobatidi 
Sharks in this respect too, and have the nostrils entirely separated fr< 
h Hence the name of Hypotr ernes, applied by DUmeril to the 
oblique or horizontal position they occupy in the other 
Rays. The skin too is smooth during youth in most 
of these fishes, and in older specimens is commonly 
shagreened on the tail alone or also on the bases of 
the pectoral fins, but sometimes over the whole body. 
The family derives its name from the form and molar 
function of the jaw-teeth, which are adapted for the 
and Pristidce) between the Rays and Sharks are approximated to the 
the mouth. 
suborder of the Rays. 
