THe INFLUENCE oF LIGHT ON ORGANS 433 
We must therefore conclude that not all the rays of diffuse 
daylight influence the formation of polyps equally, but that 
only the more refrangible (blue) rays of the visible spectrum 
favor the development of polyps, while the less refrangible 
(red) rays act as darkness—a fact similar to that established 
for heliotropism. 
3. We may finally raise the question whether or not light 
influences the development of Planula larvee. My studiesin 
this direction are not yet completed, but I found that in 
isolated cases, in spite of an exposure to darkness for several 
weeks, during which time no new polyps were formed, the 
development of the larvee progressed as under normal condi- 
tions; at least they were normal and not retarded in their 
development. I was able to make some experiments with 
the larvee themselves. These larve are pear-shaped, and are 
able to move forward very slowly by means of cilia. They 
are, as I have already shown, energetically positively helio- 
tropic. The blue rays are in these experiments more effective 
than the red. About forty-eight hours after they begin to 
swim, the larvee attach themselves to some solid base, and 
within the next twelve hours their pointed ends begin to 
grow and to form polyps, while their blunt ends form roots. 
When lighted from one side only the whole organism bends 
toward the light. The question therefore arose whether the 
Planula larva can develop a polyp in the dark. This is the 
case when a larva has developed in the presence of light. 
When brought into the dark such a larva develops a polyp 
within twelve to twenty-four hours. In this, however, we need 
not see any contradiction to the other experiments, as in 
these the development of the polyps required three to four 
days. It would be interesting to determine whether Planula 
larvee, if their whole development occurs in the dark, can 
develop polyps in the absence of light. 
Tn conclusion I wish to mention that the polyp-bearing 
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