1gor | BRIEFER ARTICLES 427 
ontogenetic, leads to more definite and concrete conclusions. Both 
views equally assume the fact of evolution in the phylogenetic fixation 
of metamorphoses, but both are equally independent of the exact 
method (the dynamics) by which that evolution is brought about, 
whether this be through natural selection involving the whole organ- 
ism, or through germinal selection, or through organic selection, or 
through the accumulation of transmitted effects of individual irritable 
responses, or through some other method still unknown. The realistic 
system, however, brings us more nearly face to face with the problems 
of the dynamics of evolution than does the idealistic system. 
We pass next to an attempt to deduce the fundamental or cardi- 
nal principles of morphology. Of these, some are not peculiar to 
morphology alone, but belong equally to other phases of evolution 
and adaptation, while others are especially characteristic of mor- 
phology. 
First, the eeible ¢ of continuity of origin, that is, no functional 
Structure ever arises de novo, but only from the modification of a pre- 
existing structure, which in turn arose from a still earlier, and so on 
backward through a longer or shorter chain ending only in the original 
protoplasmic variation, or in whatever it is which does lie at the begin- 
ning of specialization. This aia is axiomatic for both systems 
of morphology. 
SECOND, the principle of spiortiaia that is, the direction taken 
in metamorphosis is not determined by obedience to any pre-formed 
plan, but, except for the influence of the inertia of the heredity of the 
particular part, follows the factors potent at the moment. Heredity of 
itself cannot impose any plan, for it is but the summation of the inter- 
action of past experiences with original properties. ‘Theoretically this 
Principle should be as acceptable to the idealistic as to the realistic 
‘morphology. In practice, however, the idealistic conception of meta- 
morphosis as a whole is that of a play of a very few highly plastic 
“members,” which, however much they may vary and combine, retain 
a sort of fundamental immutability of nature, as witness the efforts to 
explain all parts of the flower in terms of “leaves” and “stem,” and 
the use of the expression “disguised” often applied to metamorphosed 
parts. There is thus imposed upon metamorphosis a sort of ideal plan, 
aplan implying that modification keeps within certain limits, deter- 
mined by the possibilities of permutations and combinations of those 
members. The realistic morphology is bound by no such conception, 

