Behavior of Tubicolous Annelids 159 
experiments that I was greatly puzzled. ‘The specimens were left 
until the following day when the tests were repeated, and with 
similar results though with considerable variations among individ- 
uals. 
It occurred to me that these strangely negative results might be 
in some manner related co the unusual depths from which they 
had been taken. Accordingly I secured a single specimen from 
about the docks, and hence from an unusually shallow habitat, 
and placed it in the same aquarium with the others. ‘This speci- 
men behaved quite as had those of the former year, protruding its 
crown of gills promptly, and showed the same prompt and con- 
stant response to shadow stimuli as had been observed formerly. 
This suggested at once a series of comparative studies of speci- 
mens taken from various depths. ‘The results of these experi- 
ments are shown in part in the accompanying tables to which 
detailed reference will be made slightly later. Variously tested 
both by artificial and natural light as before, the reactions of the 
shallow water specimen were incomparably more acute and con- 
stant than any of the specimens from the deeper waters. 
In order to secure a more critical comparison of the relative 
sensory qualities of these specimens they were arranged in an 
aquarium on my laboratory table so placed in relation to both 
natural and artificial illumination as to enable one to easily con- 
trol either, as to relative intensity, at will. “othe ordinary shadow 
tests produced by the interposition of a screen as in the previous 
experiments, the behavior showed the same diversities as have 
already been noticed. In order to have the tests as nearly identical 
as possible in character, and at the same time within easy control, 
it was decided to use the stimulus of the suddenly extinguished 
electric lamp, as referred to above. By this means it was quite 
easy to have all the specimens in similar conditions of expansion 
when a test was made, and by the ease with which the light might 
be extinguished, and the equal ease by which it could be turned 
on again almost instantly, one may clearly determine at a glance 
what specimens had responded and any which had failed to so 
react. 
Usually a given interval was allowed to intervene between any 
