BOTANY: W. J. V. OSTERHOUT 
237 
a transparent spot in the test and wandered inward or become altogether 
effaced. In the Cambrian trilobites, the tubercle, for the most part, is 
also absent; the median eye from the present evidence, being still in 
its most primitive form of one or two transparent spots of the test. 
It is a distinct fact pointing to a visual function of the median tubercle 
that the genera usually considered as blind because of reduced or absent 
lateral eyes, are apt to show these median eye tubercles most distinctly, 
as notably Cryptolithus, Trinucleus, Dionide, Dindymene, and also Ag- 
nostus, Microdiscus and Ampyx, while on the other hand the genera, 
Pkacops and Dalmanites with their highly developed lateral eyes, show 
the least trace of the median eye. Its constant presence in a great 
number of genera is further evidence of its important function; and 
finally the fact that all lower crustaceans typically possess the median 
or parietal eye and that for that reason zoologists of standing have 
already simply assumed the presence of this organ in the trilobites, makes 
it a reasonable inference that these primitive early crustaceans should 
have also possessed the median eye, in at least some stages of their 
evolution, and that is what the writer hopes to have demonstrated. 
A fuller account of this investigation is being printed in a New York 
State Museum Bulletin. 
THE NATURE OF MECHANICAL STIMULATION 
W. J. V. Osterhout 
LABORATORY OF PLANT PHYSIOLOGY. HA'^VARD UNIVERSITY 
Received by the Academy. March 13. 1916 
The effects of certain kinds of stimuli can be referred directly to 
chemical changes which they produce in the protoplasm, but there are 
other kinds which appear to operate by physical means only. In the 
latter category are such stimuli as contact, mechanical shock and gravi- 
tation. While their action appears at first sight to be purely mechanical, 
they are able to produce effects so much hke those of chemical stimuli 
that it appears probable that in every case their action must involve 
chemical changes. 
The chief difficulty which confronts a theory of mechanical stimula- 
tion appears to be this, How can purely physical alterations in the 
protoplasm give rise to chemical changes? It would seem that a satis- 
factory solution of this problem might serve to bring all kinds of stimu- 
lation under a common point of view, by showing that a stimulus acts 
in every case by the production of chemical reactions. 
