No.390.] THE ECTODERM OF HYDRA VIRIDIS. 509 
when chemically stimulated. In three or four days it would be 
found contracted, and in six or seven days would macerate and 
entirely disappear. 
The case is interesting, and, as far as I know, no similar one 
has ever been recorded. It is manifestly a case of response to 
some form of radiant energy, either of light or short wave- 
length, or of some other form beyond the visible end of the 
spectrum. It would have been desirable to have carried out 
histological studies upon this material, but I was unable to do 
so at the time. 
CAMBRIDGE, Mass., Feb. 10, 1899. 
