162 Charles W. FHlargitt 
and color were fully expanded in the aquarium. Some further 
reference to this colony will be made in another connection. 
A point of more than passing moment is the fact that in almost 
every colony of these annelids, whether large or small, were to be 
found evident individual differences as to sensory response. In 
most cases there was more or less sharpness and uniformity as to 
reaction, while in others there was just as evident a degree of 
uncertainty and inferiority of response. And the same variation 
was evident in the matter of recovery time following a stimulus. 
In some individuals recovery was prompt and constant, while in 
others it was just the opposite, sluggish and uncertain. Again, 
many specimens react variously on different occasions. On some 
days there were noticeable and measurable differences of reaction 
to a given stimulus. Many of these facts are graphically portrayed 
in detail in the several tables, in connection with which they are 
briefly discussed. Attention may be called particularly to the 
striking individuality exhibited by specimens and colonies taken 
from different habitats and localities. And the wider one’s range 
of observation the more evident and significant does this feature 
become. 
PHOTIC EXPERIMENTS AND FATIGUE 
The following individual records of the reactions of three speci- 
mens tested under exactly the same conditions may serve to fur- 
ther illustrate the point here under consideration and certain. 
other features of similar character. ‘The specimens were taken 
just below tide line on the adjacent shore of Buzzards Bay on July 
20, and for convenience are designated as A, B and C. 
The specimen A was tested by the shadow stimulus at inter- 
vals of one minute, and for fifteen times in succession. In every 
case there was a prompt and positive response, the creature with- 
drawing into its tube. Protrusion was somewhat variable as to 
the time concerned, varying from ten to thirty-five seconds, but 
the results were unmistakably decisive in every instance. 
In the case of B the tests were applied at intervals of 45 seconds, 
and, as before, fifteen times in succession. In this experiment 
there happened to be five specimens in a colony, and taken as a 
