200 THE COLOURS OF ANIMALS 



growth in two or three days. The nematocysts at the 

 tips of the papillae would convey a lesson to the enemy 

 similar to that taught by the fine hairs of the 'tussocks.' 



Mr. Garstang has now tested this suggestion by 

 experiment, and he finds that fish will not attack the 

 Eolids under normal conditions. He therefore threw 

 one of them (the orange variety of Cavolina Farrani) 

 into the tank containing young pollack (Gadus polla- 

 chius), which generally swallow any object while it is 

 descending to the bottom. The Eolid was swallowed 

 and rejected after a second or two by two fish, which 

 then shook their heads as if experiencing discomfort. 

 Similar movements were made when the fish were 

 induced to seize the specially defended tentacles of sea- 

 anemones, and when they attempted to swallow the 

 Poly cirrus, described on p. 201. Mr. Garstang then 

 found that the Eolid causes a distinct, though faint, 

 tingling sensation when placed on the tongue ; while 

 larger species (Facelina coronata and Eolis Alderi) 

 produce much more marked effects. 



The protectively coloured Opisthobranch, Hermeea 

 (see p. 70), has well-developed defensive papillae, 

 and Mr. Garstang finds that whenever a shadow 

 passes over it, the head is at once retracted, and the 

 papillae rendered very prominent. This behaviour is 

 exactly similar to that described in the larvae of Orgyia 

 (see pp. 197-98). The reaction under the stimulus 

 of light is associated with the unusually large eyes of 

 the genus. 



