404 The American Geologist. June, 1892 
acteristic of existing members of that stem bad been acquired, and which 
has paralleled more or less exactly the characters of the Pecora in certain 
particulars; ¢. g., the condition of the auditory bullz and the constitution 
of the posterior cannon-bone.” 
The remainder of the paper consists of two discussions: one “On che 
mode of evolution in the Mammalia,” the other “On some factors in the 
evolution of the Mammalia.” 
The first of these is concerned chiefly with the paleontological evidence 
for parallel and convergent evolution. The evidence seems quite con- 
elusive that both modes have obtained, and “it follows with great proba- 
bility that many generic groups are not real expressions of relationship, 
but artificial assemblages of similar forms.” The author points out the 
fallacy of Huxley’s dictum that “it is more important that similarities 
should not be neglected than that differences should be overlooked.” 
The evolution of the types selected for study, though with some fluctu- 
ation, is comparatively direct, and the plasticity of mammals is believed 
to show marked limitation. “In every formation, the majority of species 
appear to die out without leaving any successors behind them, and too 
early a specialization would seem to be fatal to the perpetuation of a 
group. With rare exceptions the progenitors of permanent lines seem 
to be those forms which have not strayed too far in any direction from 
the safe middle course.” 
To the general rule that among mammals differentiation is by reduc- 
tion in the number of parts, exceptions are noted; and the probability is 
indicated that evolution does not always proceed at a uniform rate. 
The part “On some factors in the evolution of Mammalia” deals chiefly 
with Weissman’s theory of heredity and the “dynamic theory.” While 
commending the former as having called renewed attention to funda- 
mental questions, the author does not accept it, considering that it con- 
fuses, rather than explains, the phenomena of heredity. The “dynamic 
theory,” on the other hand, though presenting a difficulty in understand- 
ing how changes in the periphery can modify the germ-plasm in such a 
way as to reproduce the new characters in the offspring, is regarded as 
much more consistent with the data of paleontology. 
RECENT PUBLICATIONS. 
Il, Proceedings of Scientific Societies. 
Proceedings of the Colorado Scientific Society, Vol. 111, Part 11, 1890, 
contains: Identification of Dinosaurs from the Denver Group, by Geo. 
L. Cannon, Jr.; A Remarkable Crystalline Compound of Arsenious and 
Sulphuric Acids, by Richard Pearce; Iron-Ore Beds in the Province of 
Santiago, Cuba, by F. F. Chisholm; Gold Deposits in the Quartzite For- 
mation of Battle Mountain, Colorado, by F. Guiterman; Geology of the 
Rosita Hills, Custer Co., Colorado, by Whitman Cross; Fulgurite from 
the Spanish Peaks, by R. C. Hills; On-the Nature of the Chemical Ele- 
