HYDROIDS 185 



controlled by a nervous system composed of ectodermic 

 sense-cells and a nerve-net, such as is commonly met with 

 in many ccelenterates (Wolff, 1904; Hadzi, 1909). 



Of the effectors of Corymorpha, the muscles are the 

 only elements that are under nervous control, a condi- 

 tion that supports the conclusion of Lipin (1911), that in 

 the hydroid Polypodium aside from the muscles no other 

 histological elements are dominated by the nervous 

 system. 



In attempting to study nervous transmission in Cory- 

 morpha various stimuli were first tested. Corymorpha, 

 like Tubularia (Pearse, 1906), is apparently quite unin- 

 fluenced by light (Torrey, 1902, 1904 &). Though heat 

 and some chemicals are stimulating (Torrey, 1904 &), 

 these means of inducing reactions are not so easily con- 

 trolled as mechanical stimuli. But even here a tremor 

 may be transmitted from the part of the body touched to 

 a distant receptor and thus call forth deceptive responses. 

 For stimulation a faradic current was therefore used. 

 The electrodes for this could be set in place and, after 

 all possibility of accidental mechanical disturbance had 

 passed, the intended stimulus could be applied by simply 

 making the current, thus avoiding any complication from 

 possible tremors. A well localized and controllable stim- 

 ulus was thus obtained. 



If a proximal tentacle of CorymorpJia is gently 

 touched by a blunt glass rod or stimulated by a very weak 

 faradic current, it will in a second or so after the appli- 

 cation of the stimulus bend rather quickly toward the 

 proboscis, after which it will slowly return to its resting 

 position. A more vigorous stimulus will excite to action 

 not only one but many of the proximal tentacles (Torrey, 

 1904 &) ; the proboscis is also very likely to turn in the 



