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THE 
AMERICAN NATURALIST 
Vor. XXVIII. August, 1894. — ps 332 
THE ORIGIN OF THE VERTEBRATE SKELETON. 
By J. S. KixcsrEy. a 
Until a very recent date, not a doubt existed that any part 
of the vertebrate skeleton was of other than mesodermal origin. 
The cartilages were mesoderm, and in their further develop- 
ment the cartilages were transformed into bone by means of 
the cells from the same parent layer. The membrane bones of 
the skull were also believed to mesodermal, since the re- 
searches of Oscar Hertwig (’74) had shown that in the Batra- 
chia especially, as well as in other forms, they arose from the 
layer which formed the dentine of the teeth, and which was: 
homologous with that which formed the dentine of the placoid - 
scale. The details of this need not be given here, as they will 
will be found in every text-book; the point to be emphasized - 
is that dentine and its homologue membrane bone were as- 
sumed to be, and even thought to be proved to be, of — 
mal origin. : 
One of the first papers to lay a foundation fora different view __ 
was one by Kastschenko (’88), which, while saying nothing vi me 
the origin of the skeleton, pointed out that certain parts of the - 
mesenchyme were of ectodermal origin. Next, another Rüs-' x 
sian, Goronowitsch (92), showed that in the formation of the 
* ganglionie folds" into the head, not all the tissues proliferated 
from the ectoderm into the “ —— iii was -r es 
