404 The American Naturalist. [May, 
Goette objects to the views entertained by Cope, Baur and 
myself, since they lead to the conclusion that the vertebre are 
not homologous throughout the various groups of vertebrates. 
They do not need to be homologous and are not so. The ver- 
tebral centra of the sharks, arising as they do from the inva- 
sion of cells into the elastica interna, cannot be homologous 
with those of the Teleostomes, which originate in a skeletogen- 
ous tissue outside of the elastica externa. An abnormal ver- 
tebra of the tail of Amia formed by coalescence of the two disks 
of asomite, is not homologous with one of the disks, even if 
we were, with Goette, willing to regard the latter as vertebra. 
Nor is a simple vertebra of the dorsal region, made up as it is 
of parts of two alleged vertebree, homologous with anything 
that we find in the tail. 
Of course, Goette holds that the “ primary vertebral centrum” 
is found in all the Digitata, and is developed wholly independ- 
ent of the arches. So far as the Amphibia are concerned, I 
believe that the centrum is primitively derived from the arches, 
even in the fossil Branchiosauride. We do not need to sup- 
pose that cartilage has, in all cases, surrounded the notochord 
where bone is now found. Asin Amia, the ossification may 
spread from the bases of the arches into the soft connective tis- 
sue lying against the notochord. It may even beso precocious 
in its appearance as to suppress the cartilaginous stage of the 
arches, as is the case with many fishes. 
I find that in the young Amia a thin layer of cartilage is 
formed under the bone of the centrum, lying close against the 
elastica. It appears to spread from the bases of the arches, 
and is developed later than the bone. Possibly the ancestors 
of Amia possessed a more exstensively developed condition of 
this cartilage. . 
A comparison of the early condition of the vertebral column 
of the Urodeles with that of Lepisosteus brought me to the con- 
clusion that the intervertebral cartilages of both are homolog- 
ous with the “intercalated cartilages” of Amia, and Dr. Gadow 
in a recent publication has adopted the same view. Without 
attempting to explain all of Hasse’s and Field’s results, I 
believe that they are entirely in error when they affirm that 
