the term Homology in modern Zoology. 37 
extent that there is homogeny between the chain of nerve- 
ganglia of Arthropods and the sympathetic ganglion-system 
of Vertebrata—merely an agreement which is so general that 
we can only say that the nervous system as such in the two 
cases is in the most general way homogenous, and must seek 
for some other cause to account for the more detailed resem- 
blance of the insect’s nerve-chain to the vertebrate s pa- 
thetic. In this case we see that in discussing so-called 
which segmentation of the lower jaw and suspensorium had 
been carried to a very small extent. o, too, with regard to 
the homologies of the same bones with the Sauropsidan sus- 
pensorium*. The homogenetical agreement can be one of no 
greater detail than is indicated by the condition of this region 
in the supposed common ancestor of Mammalia and Saurop- 
sida; and it does not appear probable that the incus and mal- 
eus, or the quadrate and articulare, were represented by simi- 
larly segmented bones in their common. ancestor. To take 
another case, the four cavities of the bird's heart are generally 
regarded as homologous with the four cavities of the mamma- 
uxley on the homologies of the malleus and incus and neigh- 
acceptable if we recognize homogeny, since he dwells 
Lim : 
"(of fish ndoubtedly to potential hard parts in the 
Ea Jie ana of the pe " (Brit. Med. Journ. (Abstract) 1869, 
P. 375). 
