STIMULATIONS IN NUDIBRANCHIATE MOLLUSKS 



443 



animal responds to a stimulus negatively, the appliance of it in 

 front of a progressively moving animal may bring it to a halt; 

 the directions of its movements may also be changed. 



4. The following table shows the comparative response of the 

 oral and dorsal tentacles of Hermissenda to a piece of gonads of 

 Cucumaria japonica Semper. The difference is practically 100 

 per cent. 



TABLE 4 



If this table is compared with the results as given in table 2, 

 Uu-Zz, pp. 437-438, it is seen that the oral tentacles have the 

 power of discrimination between certain substances, such as food 

 and odorous oils, while the dorsal tentacles lack this power for the 

 same substances. There is no e\ddence that the 'rhinophores' 

 are olfactory in function. 



5. The dorsal tentacles of Dendronotus giganteus, like those 

 of Hermissenda, are the most sensitive parts of the body to 

 tactile stimuli (table 3). 



6. In ]\Ielibe leonina Gould the cirrhi are more sensitive to 

 tactile stimulus than are the dorsal tentacles. 



