42 Gencral Notes. : [January, ` 
pact, hence we find no specialization of structure for counteract- 
ing, or rather for preventing injuries which such impacts might 
cause, as we find in hoofs, corneous pads or soles, nails and claws, 
but the whole impinging surface of the osseous supporting struc- 
ture is differentiated or developed in degrees ; in general terms it 
is most developed proximally and gradually shades off, becom- 
ing least developed distally. Again, in the fish but little osseous 
tissue is found developed anywhere except in opposition to the 
lines of greatest mechanical resistance encountered in locomotion, 
so that paradoxical as it may appear, it looks as though the means 
of locomotion have actually been cumulatively and ‘phylogeneti- 
cally developed by the means used to effect the movements. 
this way we may probably explain the bilaterally symmetrical 
disposition of the osseous part of the soft rays which are thickest 
where the resistance is theoretically the greatest. On the other 
hand, the volant types, which are provided with interdigital alar 
membranes, have their bones of the ordinary type, that is, ossified 
alike on all sides, hence essentially tubular; in the Pterosauria the a 
walls of the tubular digital bones are very ‘thin but dense, which — 
is in agreement with the gainer of their environments and 
is probably caused by thet 
As a non-teleological piece the following principles are ~ 
' derived : 
1. In proportion to the degree of resistance or density of the 
medium traversed, do osseous segments tend to be abbreviated _ 
and vice versa. (This tendency is only overcome by means of | 
relatively great muscular specialization, as in the long-limbed _ 
‘Anourous Batrachians and Ungulate Mammals, but even here the | 
remote impinging elements tend to become shorter. a 
a e tendency to the development of osseous structure in the 
lines of greatest resistance seems to be an invariable phenomenon — 
attending the exhibition of vertebrate life on our planet, andin | 
this way ' bilateral symmetry of the osseous halves of soft fin-rays 
is accounted for, and on the self-evident assumption that the ryth- 
mical efforts exerted in opposite directions in overcoming inertia _ 
_are potentially alike, the morphological effects tending from this 
cause to be repeated on opposite sides of a part or the. whole of _ 
the body as the case may be. The general truth that bone is de- _ 
veloped ecto-chondrially is accordingly in large part explained. 
e segmentation of limbs, of the notochord of arthropods, 
etc., into series of phalanges, vertebrae, osteomeres, neuromeres, 
myomieres, renomeres, antimeres, somites, etc., becomes clearly sub- 
ordinate to the foregoing. : 
: It will be apparent to those familiar with a sufficiently great 
-~ number of animal types and structural features that the above, a 
tivity existing between living forms and their environment, will 
a away deductively the origin of a avers majority of the 
