274 The American Naturalist. [April, 
primary conditioning factors are further modified by changes 
in the physiological processes incident to gestation. While 
these points just insisted upon must be borne in mind in work- 
ing out a final interpretation of the method of evolution of the 
various forms of the placenta, the quadrate placenta of the red 
squirrel appears to be of great significance, as bridging the gap 
between the discoidal and zonary forms ; it plainly shows how 
the passage from the one to the other was effected. This is all 
the more interesting from the circumstance that both square 
and round forms are met with in one and the same order, but 
in different suborders. 
Recently my views as to the origin of the amnion and pla- 
centa have been criticized by Minot in the Journal of MorpJiol- 
ogy, ii., pp. 432-434. In reply, it may be said that my theory 
of the amnion has little in common with that of Van Beneden 
and Julin, which is the reason I did not cite them. My theory 
of the origin of the amnion, despite my critic, remains the only 
one which is tenable. In the same way, my theory of the gen- 
esis of the girdle-like placenta is equally safe from annihilation 
at the hands of morphologists. As I entertain a great respect 
for a vast mass of data which might be cited in proof of my 
position, I should be doing less than my duty not to insist 
upon standing by the latter. — J. A. Ryder. 
PHYSIOLOGY.' 
Effects of Stimulating Nerve Cells.— The fact that 
activity of a gland cell produces in the cell protoplasm 
changes, which may be recognized by the microscope, has 
long been known. Not only is the morphological appearance 
altered, but also the behavior of the cell toward staining 
reagents. The highly interesting fact that analogous changes 
accompany the activity of nerve-cells has been discovered by 
Donaldson and Hodge' in the case of the cells of the poste- 
rior root ganglia. Korybutt-Daszkiewicz' of the Warschau 
Pathological Laboratory endeavors to advance the subject 
one step further by showing that the activity of the cells of 
' This department is edited by Dr. Frederic S. Lee, Bryn Mawr College, 
Bryn Mawr. Pa. ' ^ 
\ ^I- , ^H ^'"r^^" Journal of Psychology, Vol. i, p. 479. 1888. 
