1907-1908.] 



75 



fixing the tentacles and head to an object or to a point of the 

 stratum some distance from its base and dragging the latter up to 

 the tentacles. A very peculiar "escape" movement took place 

 on long-continued stimulation mechanically or electrically. This 

 was a kind of slow tumbling, and of a different nature to the 

 " escape " movement shown by certain infusorians, Paramecium or 

 Stentor, not being the mere result of stimulus, since as many as 

 fifty stimuli cause usually but as many mere contractions. This 

 might point to some kind of a recognition of adverse circum- 

 stances, and was certainly remarkable in an animal which showed 

 no aggregation of nerve units whatever. The chemical reactions 

 resembled simple mechanical reactions, and accounted for the 

 grasping of the tentacles on food material. The stinging cells 

 contained a coiled lasso bathed in some poisonous fluid, which 

 was thrown out when the animal is irritated. Chemical irritation 

 was necessary, not, as usually thought, mere mechanical disturb- 

 ance of however severe a kind. A point which had not hitherto 

 been noticed in the movements of Hydra was that it did not 

 contract en masse, but in fractions, one-third or one-quarter of its 

 length at a time. As Professor Gregg Wilson pointed out, this 

 might be due to a segmental arrangement of muscle spindles in 

 the body walls. Here they had indications of segmentation in 

 the very first of the Metazoa. The animals showed "light" 

 reactions, due no doubt to the green chlorophyll corpuscles in the 

 endoderm, this being one of the few cases where plant pigment 

 occurred in the animal world. (Applause.) The lecturer then 

 invited his audience to examine specimens of Hydra under the 

 microscope, which was largely availed of, the curious and 

 beautiful animals creating much interest. 



A very interesting discussion followed, in which the 

 following took part : — Miss E. Andrews, Professor Gregg 

 Wilson ; Messrs. William Gray, M.R.I. A.; Robert Welch, 

 M.R.I. A. ; and Robert May, after which the proceedings 

 concluded. 



