LR. Hitechcock— Causes of Variation. — 49 
comparative width of the dorsal depression. Its movements 
are similar to those of S. apocamptus, the long flagellum being 
held somewhat more obliquely than with that species. The 
body is frequently elevated during its progression so that the 
apex seems to be held in contact with the slide, a position not 
observed with S. apocamptus. The anterior body half is trans- 
parent; colorless corpuscles and green food-particles collected 
posteriorly render that part semi-opaque. 
Trenton, N. J. 
Art. VIII.—The Causes of Variation ; by Romyn HircHcock. 
THE recent studies of Dr. W. B. Carpenter Hie Orbitolites, 
which were noticed in the April number of this Journal, are 
of special interest owing to the remarkable manner in which the 
stages of variation and development have been traced. The 
monograph by Dr. Carpenter, published in the Reports of the 
leat Expedition, was the subject of some remarks 
ture in the calcareous fabri This, however, is merel 
Statement of the facts siaerrell and in heb assists in 5 a 
aan or ‘aimless’ variation. 
The facts seem capable oe a somewhat different interpretation, 
which seems mort in accord with our present knowledge o 
simple organisms, and quite sustaining the views of Darwin 
that “plan,” in the sense used by Dr. Ourheuter, should 
Superfluous. For if there be an inherent tendency to variation 
among these organisms, as Dr, Carpenter seems to believe, how 
do we explain the persistence of the original orbitoline type 
tenuissima ? Biologists seek to discover the causes of variations 
which they observe, but it seems not less important that the 
persistence of types ‘should also be explained. 0. tenuwissima is 
a very ancient species, and surely any inherent tendency to 
change would have manifested itself during the long period of 
its existence, even under unfavorable conditions, 
he observations I have to offer may be said to relate 
entirely to change of environment, but their seadeney, is to 
Am, JOUR Sy ET es — Vou. XXVIII, No. 163.—Juny, 1884, 
