and its Significance in Systematic Zoology. 85 
Gould) ; and the true Kangaroos (Macropus) are equally nearly 
approached in form by the Cape Leaping Hare (Pedetes capensis, 
Ill). There is also a considerable resemblance between the 
Wombat or Badger of the Australian colonists (Phascolomys 
Wombat, Pér. and Les.) and the Rodent Cavies and Lagomys ; 
while a further homomorphism occurs between individuals be- 
longing to aberrant groups in either Order, viz. the Brazilian 
Porcupine (Synetheres) among the Rodents, and the Echidna 
among the Monotremes, whose relation to the Insectivora has 
already been pointed out. 
These external resemblances between Rodents and Marsupials 
are none the less remarkable when we learn that there is less true 
affinity between them than between the Marsupials and most 
other Orders; for Mr. Waterhouse, in his excellent ‘ History of 
the Marsupialia,’ remarks that in them “we find representatives 
of most of the other Orders of Mammalia. The Quadrumana 
are represented by the Phalangers; the Carnivora by the Da- 
syuri; the Insectivora by the small Phascogales; the Rumi- 
nautia by the Kangaroos, and the Edentata by the Monotremes.” 
He adds : “ The Cheiroptera are not represented by any known 
Marsupial animals, and the Rodents are represented by a single 
species only” —the species referred to being the Wombat. 
Lastly, the Marsupialia, besides their homomorphism with 
the Rodents, have, through the Ursine Opossum, or Native 
Devil of Van Diemen’s Land (Dasyurus), a singular relation- 
ship to the Carnivorous genus Ursus, as well as, through the 
Squirrel Petaurus, to the Bats. 
Space will not permit me to compare the forms of Inverte- 
brata one with another. Among them many remarkable analo- 
gies of form may be observed ; and even between the Vertebrata 
and Invertebrata they will be found to occur. Further illustra- 
tions of this subject may be found in a paper by the author in 
the ‘ Proceedings’ of the Liverpool Literary and Philosophical 
Society for the past session. 
On no principle of gradation of form can these resemblances, 
unaccompanied as they are by homologous relations, be accounted 
for. Some are advances, others degradations of form ; and we 
must look for some deeper and more subtle cause which shall 
connect animals so widely separated as are the members of 
distinct subkingdoms. There is one circumstance, however, 
which cannot fail to strike the thoughtful inquirer, and which, 
I think, holds out a clue to the remarkable facts to which I 
have just now briefly alluded. ‘The circumstance to which I 
refer is, that, in not a few cases, striking deviations from typical 
form are accompanied by no less striking modifications of typi- 
cal habits; and further, that these modified habits have a strong 
