e spends, and in what way.
Thrice happy art thou, Walden, in thyself!
Such purity is in thy limpid springs,--
In those green shores which do reflect in thee,
And in this man who dwells upon thy edge,
A holy man within a Hermitage.
May all good showers fall gently into thee,
May thy surrounding forests long be spared,
And may the Dweller on thy tranquil marge
There lead a life of deep tranquillity,
Pure as thy Waters, handsome as thy Shores,
And with those virtues which are like the Stars!"

METHODS OF STUDY IN NATURAL HISTORY.

VII.

I come now to an obscure part of my subject, very difficult to present
in a popular form, and yet so important in the scientific investigations
of our day that I cannot omit it entirely. I allude to what are called
by naturalists Collateral Series or Parallel Types. These are by
no means difficult to trace, because they are connected by seeming
resemblances, which, though very likely to mislead and perplex the
observer, yet naturally suggest the association of such groups. Let me
introduce the subject with the statement of some facts.

There are in Australia numerous Mammalia, occupying the same relation
and answering the same purposes as the Mammalia of other countries. Some
of them are domesticated by the natives, and serve them with meat, milk,
wool, as our domesticated animals serve us. Representatives of almost
all types, Wolves, Foxes, Sloths, Bears, Weasels, Martens, Squirrels,
Rats, etc., are found there; and yet, though all these animals resemble
ours so closely that the English settlers have called many of them by
the same names, there are no genuine Wolves, Foxes, Sloths, Bears,
Weasels, Martens, Squirrels, or Rats in Australia. The Australian
Mammalia are peculiar to the region where they are found, and are all
linked together by two remarkable structural features which distinguish
them from all other Mammalia and unite them under one head as the
so-called Marsupials. They bring forth their young in an imperfect
condition, and transfer them to a pouch, where they remain attached to
the teats of the mother till their development is as far advanced as
that of other Mammalia at the time of their birth; and they are further
characterized by an absence of that combination of transverse fibres
forming the large bridge which unites the two hemispheres of the brain
in all the other members of their class. Here, then, is a series of
animals paralle