9\ 7 I= 
1871.] 245 [Cope. 
In by far the greater number of animals these kinds of repetitive struc- 
ture coexist. The longitudinal is however predominant inthe Vertebrata, 
Mollusca and Articulata, while the centrifugal is greatly developed in the 
Celenterata and Radiata. In none but the simplest forms, are either of 
these modes to be found alone. 
The centrifugal repetition or addition, more nearly resembles the mode 
of aggregation of atoms in inorganic or crystalline bodies, and hence may 
be regarded as the inferior manifestation. It implies that growth force 
in this case conforms to a law of polarity in exhibiting itself at equal dis- 
tances from a centre,—which is allied to ordinary molecular force, and in- 
dependent of the localizing influences of which higher organisms seem 
capable. In centrifugal animals, then, the latter evidently plays an in- 
ferior part. In Coelenterates and Radiates, however, the body possesses a 
short longitudinal axis, in some /Asterias) very short, in others (Holothu- 
ria), more elongate. The amount of complication of centrifugal growth 
greatly exceeds the complication in a longitudinal direction mal Or 
these animals.except the Holothurida. 
It is now important to observe that great numbers of centrifugal ani- 
mals are sedentary or sessile; while the longitudinal are vagrant, moving 
from place to place. Many of the centrifugal animals which wander, do 
not do so in in the direction of their axis, but sideways (Medus«). It is 
also proper to notice that not only the movements of the muscles, but also 
the direction taken by the food is in the long axis. It is therefore to be con- 
cluded that in longitudinal animals growth force has assumed a more truly 
animal type, and that this tendency has predominated over the polar or 
molecular tendency. 
In most longitudinal animals, however, certain lateral portions, limbs, 
etc., extend on each side of the axis; and were the space marked by their 
extremities, and those of the axis, filled, we would have the outline of a 
centrifugal animal. 
Before discussing the influences which have increased and located 
growth force, it will be necessary to point out the mode in which these 
influences must necessarily have effected growth. Acceleration is only 
possible during the period of growth in animals, and during that time 
most of them are removed from the influence of physical or biological 
causes, either through their hidden lives or incapacity for the energetic 
performance of life functions. These influences must, then, have opera- 
ted on the parents, and become energetic in the growing fotus of the 
next generation. However little we may understand this mysterious 
process, it is nevertheless a fact. Says Murphy, ‘‘ There is no act which 
may not become habitual, and there is no habit that may not be inher- 
ited.’”? Materialized, this may be rendered—there is no act which does 
not direct growth force, and therefore there is no determination of growth 
force which may not become habitual; there is, then, no habitual deter- 
mination of growth force which may not be inherited ; and, of course, in 
a growing fotus becomes at once energetic in the production of new 
s tructure in the direction inherited, which is acceleration. 
