1888. | NEW YORK ACADEMY OF SCIENCES. 257 
are correct, then the barbels of fishes must be phylogenetically 
derived from the papille of a suctorial disc adjoining the 
mouth.” 
Of Lepidosteus, he says :* ‘‘On the ventral surface of the front 
of the head there is a disc which is beset with a number of pro- 
cesses, formed as thickenings of the epiblast. As shown by 
Agassiz, these eventually become short suctorial papille.” 
‘‘The young fish on hatching immediately uses its suctorial 
disc to attach itself to the side of the vessel in which it was 
placed.” * 
Describing the suctorial discs of the Anura, he says: “ ‘They 
are probably remnants of the same primitive organs as the suck- 
ing dise of Lepidosteus.” * 
If the homologies suggested in these extracts are correct, we 
have in the preoral processes just described, representatives of 
external branchiw, and we have them also in the barbels of 
fishes and of the larvee of Dactylethra.* 
The labial cartilages may probably represent the remains of 
an extra-branchial system connected with them. 
The cilia on the gills, as on the body, are arranged in raised 
clusters, which bear a close resemblance to, and are bdoutless 
homologous with, the sensory organs of the lateral line. Special 
lines of these organs are present, as is well known, in amphi- 
bian laryee, and one line connects the bases of the fore and hind 
limbs. 
Gegenbaur considers that the limbs are derived from branchial 
arches and rays—a view which was held for a while by Dr. An- 
ton Dohrn. When, however, it was found that the paired fins 
‘arose as special developments of a continuous ridge on each 
side, precisely like the ridges of epiblast which form the rudi- 
ments of the unpaired fins,” ° a fatal objection was supposed 
to be offered to Gegenbaur’s view, and the theory now most in 
favor seems to be, that the limbs are derived from continuous 
lateral fin-folds. 
If, however, we regard the limbs as derived from the external 
branchiz and the extra-branchial system, the lateral fold could 
represent a series of coalesced external gills, which might be 
modified throughout its whole extent, or, it might be modified in 
1Tbid., p. 95. 
2Tbid., p. 98: 
STibids; pa lt0: 
4If asystem of preoral arches existed—and I hope in another place 
to give some evidence of a different nature from that given above, in 
favor of such a view—any effort to ascertain the number of original 
cranial segments can scarcely be crowned with success. 
5 Balfour, ‘‘ Elasmobranch Fishes,” p. 101. 
