140 On the Evolution of the Vertebrata, [ February, 
portions of the fibro-vascular systems may also serve their usual 
purpose of conductors of water. 
EXPLANATION OF PLATES, 
PLATE IV. 
Fic. 1.—Sketch of a gall showing its ordinary form, size and position. Natural 
size. 
Fic, 2.—Sketch of the gall showing its appearance when found above the first set of 
leaflets. 
Fic. 3.—Several galls on the same petiole showing the effect on stem and the gen- 
eral arrangement and shape of the galls when more than one occurs on the 
same petiole. 
Fic. 4.—Cross section of gall and petiole, showing internal appearance of gall. 
PLATE V. 
Fic. 5.—Cross sections of normal petiole; a, at base, no well-developed second row 
of fibro-vascular bundles; 4, below first pair of leaflets, appearance of second 
row of fibro-vascular tanidi c, above first pair of leaflets, a well-developed 
second row of fibro-vascular bundles 2 
ia 6.—Clustered hairs, X 165. 
G. 7.—Glandular hairs. X 165. 
A IG. 8.—Gall hairs, extensions of epidermal cells, 
PLATE VI. 
Fic. 9.—Cross section of petiole and gall; a, gall hairs which appear to be contin- 
uations of the epidermis 4; ¢, parenchyma beneath the epidermis; æg, fibro-vas- 
cular bundles in which tracheids have supplied the place of tracheary and 
other vessels; e, parenchyma of the pith (highly magnified). 
Fic. 10.—Longitudinal-radial section of petiole and gall; a, 4, c, d, e, as in fig. 9 
highly magnified). 
"ry". 
os 
ON THE EVOLUTION OF THE VERTEBRATA, PRO- 
GRESSIVE AND RETROGRESSIVE. 
‘BY E D. COPE. 
I. PRELIMINARY. 
E attempting to ascertain the course of evolution of the Verte- 
brata, and to construct phylogenetic diagrams which shall 
express this history, among the difficulties arising from deficient 
information, one is especially prominent. As is well known, 
there are many types in all the orders of the Vertebrata which 
present us with rudimentary organs, as rudimental digits, feet or 
limbs, rudimental fins, teeth and wings. There is scarcely an 
organ or part which is not somewhere in a rudimental and more 
or less useless condition. The difficulty which these cases pre- 
sent is, simply, whether they be persistent primitive conditions, to 
