732 The American Naturalist. [August, 
times in the centrosomes, and the chromosomes may appear rather as 
hollow vesicles than as solid bodies. The general protoplasm, filled 
with yolk, showed in some cases a very fine net-alveolar structure in 
places. On the surface the alveolar layer of Biitschli was always 
present, and just after the cleavage a very plain cell-plate of Carnoy is 
regarded and figured by the author as merely the appressed alveolar 
layers of the two adjacent cells. 
PSYCHOLOGY .! 
Physiological Effects of Mental Work.—Within the present 
decade the relation between mental work and the bodily processes has 
been the subject of much study. Interest in the problem as a field for 
practical inquiry was first aroused by a paper on the fatigue resulting 
from intellectual work, published by Sikorsky in the Annales d'hygiène 
publique for 1879. He was followed more than ten years later by 
Burgerstein, Laser, Griesbach and others. In these investigations the 
method used was that of testing school children in classes. Various 
problems and exercises were set before them, during and after the 
school session, and the percentage of errors committed in the operations 
was taken as measure of the fatigue due to mental work. While some 
individual errors might be due to other causes, the average percentage 
of the entire class seemed a fair test of this factor. The latest instances 
of this method are the investigations of Friedrich and Ebbinghaus de- 
scribed in the May number of the Naturauist. At about the same 
time Mosso and his pupils took up the question from another side. 
They instituted a series of laboratory investigations upon single indi- 
viduals by means of the ergograph, with a view to determining the 
fatigue due to steady intellectual, as well as physical work. Kraepelin 
and his pupils meanwhile undertook the same problem, varying it with | 
tests of the influence of various stimulants and narcotics on the capac- 
ity for mental work. They made use of the reaction time method, as 
well as the percentage of errors. More recently, Binet and his pupils 
have taken up the subject from a different standpoint, their object be- — 
ing to measure the effect of mental stimulation and mental effort on the 
bodily processes of breathing, heart action, ete. Several other investi- 
1 Edited by Howard C. Warren, Princeton University, Princeton, N. J. 
