4 The First Lines of Morphology 
at all. Our position would indeed be altogether hopeless, were 
it not for the fact, which indeed alone renders any scientific 
inquiry possible, and sanctions it, namely, the uniformity of 
nature. But this uniformity is so great, that not only does it 
hold good in securing the recurrence of the same phenomena 
when the same conditions of existence recur; but, inasmuch 
as the Architect of nature is one, the same style of architec- 
ture prevails from the simplest to the most elaborate of all 
Nature’s works. Moreover, there can be no doubt that the 
problem would be utterly insoluble by us, did we not see it 
actually solved in nature. Nor could we proceed were we 
without the principle that the normal form, structure, and 
course of lifein every orgasm and living being must be in 
harmony with the conditions of its existence. The great value 
of this fact as a canon of biological research was first shown by 
Cuvier, and it has been generally acknowledged since his day. 
But it is possible to carry it now much farther than it could 
be carried then, and also to simplify its application. Thus, in 
order to ascertain the most general principles of morphology, 
it is not necessary to take into detailed consideration all the 
conditions of existence of living beings. It is enough to take 
into consideration the bearings upon life of the ambient 
medium in which an orgasm or living being is appointed to 
live, and by which it is constituted a member in the system of 
nature, and enters into the economy of nature. Hence, also, 
it is not necessary to consider even the ambient medium, in 
reference to its intimate constitution, or otherwise than in 
reference to the changes to which it is subject. Nay, it is not 
necessary to consider even these changes in detail, or in their 
relations among themselves, but only in their bearings upon 
the life which they touch: In a word, it is enough to regard 
them under one or other of the three categories within one or 
other of which they must all be comprised, viz., (1.) Changes 
which are unfavourable to the development of life; (2.) 
Changes which are favourable; and (3.) Alternations from 
either of these to the other, such as are constantly occurring 
during the vicissitudes of protracted existence. Now, the 
forms corresponding to these various states of the ambient 
medium, we may, in the meantime, provisionally designate as, 
