STIMULATIONS IN NUDIBEANCHIATE MOLLUSKS 439 



the normal individuals. That is, I placed a number of normal 

 specimens in a narrow trough ca. 60 cm. long, 5 cm. wide, and 

 6 cm. deep, and tilted it at one end ca. 3°, allowing a gentle 

 stream of sea-water to pass in at the raised end and out in the 

 opposite end through a sieve. Everyone oriented himself toward 

 the current and moved first against it until arriving at the end of 

 the trough. A number of individuals in which the dorsal tentacles 

 had been removed, either partly or totally, either only one or 

 both, behaved in the same manner as the non-mutilated ones, 

 save two of the ones operated on, which seemed to be a little 

 disturbed at first. Otherwise it did not seem to make any 

 difference whether the 'rheotropic' tentacles were present or not. 

 The function of the dorsal tentacles, therefore, does not seem to 

 be 'rheotropic' in Hermissenda. They are tactile organs, how- 

 ever, and may also be slightly gustatory in function. 



Type 2- — Dendronotus giganteus O'Donoghue 



I collected a single specimen of the wonderful species Den- 

 dronotus giganteus from between the logs of the floating dock at 

 the station. It measured 140 mm. in length, 60 mm. deep, and 

 the foot was 90 mm. long and 40 mm. wide. (For a complete 

 description, vide O'Donoghue, '21.) This species is much more 

 sensitive to tactile stimuli than is Hermissenda, and is, therefore, 

 not so easily experimented on. The slightest disturbance of the 

 water caused some local contraction of the body. However, the 

 following data were collected, and it may be of interest to study 

 them in comparison with those on Hermissenda (table 3, p. 

 440). 



This table (table 3) shows graphically that the dorsal tentacle, 

 the 'rhinophore,' of Dendronotus is on the whole more sensitive 

 to contact stimuli whether physical or chemical. 



Type S — Melibe leonina Gould 



One specimen of this remarkable species was given to me by 

 Dr. Elmer Lund, who found it at the floating dock. The speci- 

 men measured 65 mm. in length; the height was 10 mm., and the 



