No. 387.] THE OSSICULA AUDITUS. 227 
both Meckel’s cartilage and the palatoquadrate of the elasmo- 
branchs arise from a continuous cord of cells, and only with the 
process of chondrification does differentiation occur. In the 
digits the separate phalanges are likewise developed from a 
continuous mass of procartilage cells. In the light of all the 
evidence we feel impelled to agree with the majority of the 
embryological students who have studied the question and to 
regard the incus as the quadrate. 
It appears to us that the relations of these ear-bones throw 
no little light upon the question of the origin of the mammals, 
or at least of the so-called higher mammals, since it is not 
beyond question that the mammals are a monophyletic group. 
For many years it was the general supposition that the mam- 
mals have descended from the Amphibia. Then came the 
discovery of the meroblastic ova of the monotremes, and the 
almost simultaneous announcement of the recognition of mam- 
malian features in the theromorphous reptiles. Then for several 
years the prevailing view was that the mammals must have had 
a reptilian ancestry; but the pendulum began to swing back- 
wards. The difficulty of the double occipital condyle remained. 
Hubrecht has pointed out the difficulty of deriving the mam- 
malian ovum, with its peculiarities of segmentation, gastrulation, 
and especially its foetal envelopes, from the sauropsidan type, 
while these can readily be evolved from the amphibian egg. 
Maurer has shown that it is impossible to compare the hair, so 
characteristic of mammals, with any known structure in reptiles; 
while, on the other hand, he has pointed out the close resem- 
blances even in structural details between hair and the epi- 
dermal sense organs of the Amphibia. 
Now, when we consider the ossicula auditus we see the 
impossibility of deriving those of the mammals from those of 
the reptiles. As we have shown, the shaft of the columella in 
the reptiles is postspiracular and is below the chorda tympani, 
while the incus and the body of the malleus are prespiracular 
and are above and outside of the chorda tympani. On the other 
hand, the mammalian ear-bones with all their peculiar features 
(the manubrium of the malleus excepted) are derivable from 
those of some urodele-like form. In the urodeles, as in mam- 
