1878.| Morphological Effects of Like Mechanical Conditions. 157 
ered Europe from Portugal to the foothills of Caucasus have dis- 
appeared, the mountains of Persia have become naked rocks and 
the promised land is a desert ; but the Sunda Islands, Southern 
India, Siam, Ethiopia and the birthland of the Nile are still as 
sylvan and as prolific of life as in the springtime of creation. Not 
only the ocean but the vegetation of the tropics can defy “the 
vile strength, which man for earth’s destruction wields,” and 
Macauley’s New Zealander who might visit the desert relics of 
American cities after musing over the ruins of London, would 
still find the primeval forests that covered the southern part of 
our continent when Humboldt and Bonpland explored the valley 
of the Amazon. 
“These forests will be felled,’ says De Tocqueville, speaking 
of the Calaveras cedar groves, “they will disappear as the cedars 
of Lebanon and the mountain-firs of Scotland have disappeared ; 
these and all other forests of the cold and temperate zones. e 
trees of the tropical woodlands are the only true evergreens on 
earth.” . 
:0; 
ON LIKE MECHANICAL (STRUCTURAL) CONDITIONS 
AS PRODUCING LIKE MORPHOLOGICAL EFFECTS. 
BY JOHN A. RYDER. 
PROPOS of the interest recently manifested in the matter of 
“the relation of animal motion to animal evolution,” I have 
thought it pertinent to offer the following remarks. The possible 
morphological effects of like mechanical or structural conditions 
are illustrated in the vertebral axes of turtles and extinct armadil- 
- loes (Hoplophoride), where the rigid exoskeleton (carapace) has 
caused the originally segmented axial skeleton to exhibit a strong 
tendency to revert to the primitive homogeneous (notochordal) 
condition, without at the same time losing its osseous character. 
The exoskeleton in both these groups has assumed in part the 
function of the chitinous exoskeleton of articulates. The verte- 
bral axis relieved in both instances from the transverse flexures 
incident to locomotion and respiration, has codssified into a solid 
bony bar, or rather a hollow tube, with loss of the cylindroid 
form of centrum. The vertebral centra are in both represented 
ee 1 See E. D. Cope in this Journal for January, 1878. 
