388 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
physical facts or laws the morphologist as well as the physiologist 
may draw important consequences. 
it was Hofmeister who first showed, more than 40 years ago, 
that when any drop of protoplasm, price over all its surface or at 
some free end (as at the tip of the pseudopodium of an ameceba), is 
seen to ‘‘round itself off” that is not the effect of physiological or 
vital contractility, but is a simple consequence of surface tension— 
of the law of the minimal surface; and on the physiological side, 
Engelmann, Biitschli, and others have gone far in their development 
of the idea. Plateau, I think, was the first to show that the myriad 
sticky drops or beads upon the weft of a spider’s web, their form, 
their size, their distance apart, and the presence of the tiny inter- 
mediate drops between, were in every detail explicable as the result 
of surface tension, through the law of minimal surface and through 
the corollary to it which defines the limits of stability of the cylinder; 
and, accordingly, that with their production the will or effort or 
are oleence of the spider had nothing to do. The beaded form of a 
long, fin pseudopodium, for instance, of a Heliozoan, is an identical 
phenomenon. It was Errera who first conceived the idea that not 
only the naked surface of the cell but the contiguous surfaces of 
two naked cells, or the delicate incipient cell membrane or cell wall 
between, might be regarded as a weightless film whose position and 
form were assumed in obedience to surface tension. And it was he 
who first showed that the symmetrical forms of the unicellular and 
simpler multicellular organisms, up to the point where the develop- 
ment of a skeleton complicates the case, were one and all identical 
with the plane, sphere, cylinder, unduloid, and catenoid, or with 
combinations of these. Berthold and Errera almost simultaneously 
showed (the former in far the greater detail) that in a plant each 
new cell partition follows the law of minimal surface and tends (ac- 
cording to another law, which I have not particularized) to set itself 
at right angles to the preceding solidified wall, so giving a simple 
and adequate physical explanation of what Sachs had stated as an 
empirical morphological rule. And Berthold further showed how, 
when the cell partition was curved, its precise curvature, as well as 
its position, was in accordance with physical law. 
There are a vast number of other things that we can satisfactorily 
explain on the same principle and by the same laws. The beautiful 
catenary curve of the edge of the pseudopodium, as it creeps up its 
axial rod in a Heliozoan or a. Radiolarian, the hexagonal mesh of 
bubbles or vacuoles on the surface of the same creatures, the form 
of the little groove that runs round the waist of a Peridinian even 
(as I believe) the existence, form and undulatory movements of the 
undulatory membrane of a Trypanosome, or of that around the tail 
of the spermatozoon of a newt—every one of these, I declare, is a 
