920 
tion must be left open.’ Questions arising in 
connection with the migratory habit are left in 
a similar way. 
Professor Morgan now lays special stress upon 
consciousness as a cooperating factor in organic 
development. In the earlier chapters it was 
assumed, for the sake of simplicity, that men- 
tal evolution might be concomitant with, 
rather than a factor of, organic evolution. His 
presentation of the difference between organic 
evolution as a result of the elimination of the 
unfit, and of organic evolution as a result of 
conscious choice, through the elevation of the 
fit, is extremely ingenious, and the part that 
the latter may play in the struggle for exist- 
ence is clearly shown. ‘‘In so far as conscious 
adjustment aids in the struggle for existence, 
in so far through it the animal is better able to 
escape danger, to secure a more favorable habi- 
tat, to gain a mate and beget progeny ; the ani- 
mal possessed of intelligence will escape elimi- 
nation, transmit his power of conscious ad- 
justment, and contribute to the propagation of 
his race. Without fully subscribing to the doc- 
trine of the all-sufficiency of natural selection, 
we may yet say that natural selection will ex- 
ercise a determining influence in deciding the 
course which conscious adjustment must take.”’ 
The question of the inheritance of acquired 
habits is many times raised, but receives no 
partisan treatment in the first three hundred 
pages. In the latter part of the book the 
author instinctively holds to his earlier belief, 
while admitting, as a result of his experience, 
certain intelligent modifications of his views. 
We quote from page 305: 
‘Tf pressed to summarize my own opinion on 
this question, I should say: First, that there is 
but little satisfactiory and convincing evidence 
in favor of transmission, but that variation 
does seem in some cases to have followed the 
lines of adaptive modification, so as to suggest 
some sort of connection between them ; sec- 
ondly, that there are many instincts relatively 
definite and stable which may fairly be re- 
garded as directly due to natural selection, 
though here again, if we could accept the view 
that adaptive modification marked out the 
lines in which congenital variation should run, 
our conception of the process of their evolution 
SCIENCE. 
LN. S. Von. VI. No. 155. 
would be so far simplified ; thirdly, that there 
are some peculiar traits, also seemingly definite 
and stable, which can only be attributed to the 
indirect effects of natural selection.’’’ 
In the discussion of modifications and varia- 
tions the author follows Mark Baldwin in de- 
fining the former as acquisitions which occur in 
the course of individual life, and the latter as 
those changes in the individual which are the 
result of some disturbance in the germinal sub- 
stance. Mental phenomena are laid aside for 
a time and the more easily apprehended argu- 
ments and illustrations from structure adopted. 
The author dwells at considerable length upon 
the claims of the extreme Neo-Darwinians, on 
the one hand, and the extreme Neo-Lamarcki- 
ans, on the other, and concludes that ‘‘all this is 
very interesting, and affords considerable scope 
for ingenuity. But it does not touch the ques- 
tion at issue, and this is, not which method is 
apparently the most advantageous ; not which 
method we should have adopted had the work 
of creation been entrusted to our care, but 
which has been adopted by nature.’’ Weis- 
mann’s principles of germinal and intra-selection, 
Baldwin's organic selection and the author’s in- 
nate plasticity indicate the neutral ground where 
selectionists may meet transmissionists ; where 
fortuitous variations may finally take the place 
of mere temporary adaptive modifications. 
Professor Morgan’s entertaining style, his 
originality of experiment, his quick interpreta- 
tion, his rare quality of explanation and the 
comparative novelty of his subject will give 
‘Habit and Instinct’ a place beside ‘Animal 
Life and Intelligence’ in the library of every 
working biologist. HERMON C. BUMPUS. 
Das Nordliche Mittel-Amerika, nebst einen Aus- 
flug nach den Hochland von Anahuac. Yon 
Dr. CARL SApPER. Braunschweig, Vieweg 
und Sohn. 1897. With maps and illustra- 
tions. Pp. 436. ) 
The studies of Central American geography 
and ethnography which Dr. Sapper has con-' 
tributed to Petermann’s Mittheilungen, Globus. 
and other periodicals, from time to time during 
the last ten years, have made his name familiar 
to all interested in the products and history of 
that portion of our continent. In the volume 
