346 
PROGRESS OF ZOOLOGY. 
correspondence of mutual relationships which a system 
professes to unfold. That homologies of structure are 
to be regarded as of the first importance in the deter¬ 
mination of the place an animal is to occupy in a natural 
system is self-evident; but it is worth asking, whether a 
purely artificial system would not serve as useful a purpose 
in zoology as it has done in botany, because it could be framed 
once for all, and serve for comparison at any future time with 
a progressive natural system, which of necessity can never 
be perfect. Pliny excites the laughter of the young 
naturalist when he describes the cat as the only bird that 
suckles its young; but a strictly homomorphic system 
would have its value, and the wonder is that no one has 
ventured hitherto to propose a scheme of the kind. Bats, 
squirrels, and marsupiates claim relationship with birds in 
their faculty of flight; the quadrumanes might as well con¬ 
tribute the marmosets to the family of squirrels, and the 
Douroucouli to the cats, as retain them for the doubtful 
character of their hands. The armadillo, Dasypus apar , is 
more like a turtle than a mammal; the Aard-wolf, Proteles 
Lalandii , is a hyena in its external aspects; the Cetacea are 
fishes, to all intents and purposes, in their habits of life 
as well as in general form. Perhaps the difficulty of classing 
the marsupiates might be got over at once by homomorphism, 
for as at present regarded they threaten the boundaries of 
Rodentia, Carnivora, Cheiroptera, and Testudinata, and 
a classification resting on external configuration w r ould 
serve all the purposes of an index to species, without im¬ 
peding inquiry into physiological and anatomical details. 
As it is, the natural system affords only a few faint indi¬ 
cations of character, and the fault of all natural systems 
is that as soon as they cease to indicate correctly they lead 
the student astray, for after a few of the most characteristic 
groups have been defined—as in botany the Coniferae, the 
Cupuliferae, and the Ranunculaceae, and in zoology the 
Quadrumana, the Carnivora, and the Rodentia—there are 
innumerable other subjects that refuse to conform to distinct 
positions by reason of their combining the characteristics of 
many. No system can suffice to indicate the place, for 
instance, of that curious vertebrate, Amphioxus lanceolatus , 
which, emulating the chameleon, has a life on one side 
which has no necessary conformity on the other. The 
chameleon may sleep on the left side while the right side 
is aw^ake, and in the Amphioxus the bronchial aperture, the 
olfactory organ, and the eye, are all situated on the left side. 
The Chamcelonidce are, however, a well-defined group of 
