Vertebroid Homologies of the Cranium in Vertebralia. 59 
the humeral zone, which, in insects, carries on the haemal 
upturned aspect, the first pair of wings, appendages of the 
respiratory organs, whether lungs, branchise, trachese, &c. &c. 
The meta thoracic riog supports the hind legs, and the 
second pair of wings on the hsemal aspect, representing the 
ventral fins in fishes. 
In Crustacea the number of legs from the meso thoracic 
and metathoracic rings are doubled ; the prevertebral cara- 
pace homologous with the mammal palate completely covers 
the centres of the nervous, digestive, and vascular systems ; 
these rings are incomplete. 
A portion of Professor Huxley's " Lectures on the Verte- 
brate Skeleton" has appeared in " The Lancet," illustrated 
by diagrams in wood. These have been little consulted, 
from being inconsistent with the vertebral scope of this paper, 
based on the unity of organisation and the vertebroid homo- 
logies of the animal kingdom. Who can decide when 
doctors disagree 
On Develoj)ment as the basis of Homology. 
Agassiz, Goodsir, Huxley, and others, maintain that the 
study of the progressive development of the various laminae 
composing the skelon is the only basis on which the deter- 
mination of accurate homology can surely rest ; and Cuvier 
long ago propounded the same dogma when enumerating the 
bones in each species of the mammalia. " We must descend 
to the primitive osseous centres as they exist in the foetus." 
Owen showed the inapplicability of this rule, as the human 
brachium should be counted three bones instead of one, and 
in like manner four would be enumerated instead of the 
femur. The Cuvierian rule fails by not distinguishing be- 
tween the ossific points which permanently complete the 
bone and those which only typify parts of bones which are 
in the foetal condition separate, in order to facilitate ossifi- 
cation of individual bone, as the cases above referred to. The 
study of development having comparatively but a restricted 
sphere among anatomists and naturalists, little advantage 
can safely be taken of it, as in the present state of our 
knowledge it seems to have led as much to confusion as to 
