122 MENTAL EVOLUTION IN ANIMALS. 



of memory is also present in the division of the Mollusca. 

 The Razor-fish, likewise, shows memory, and this in a high 

 degree, inasmuch as if only once alarmed upon coming to the 

 surface of its burrow, it cannot be again induced to approach 

 the surface for a long time, even by the application of irri- 

 tants.* Still more remarkable is the level of development to 

 which memory has attained in the Snail, if the observation of 

 Mr. Lonsdale is to be accepted of the Helix pomatia, which, 

 after leaving its sickly mate and crawling over a garden wall, 

 returned next day to the place where it had left its mate.f 

 But the highest level to which the development of memory 

 attains in the Mollusca is unquestionably in the Cephalopoda, 

 for according to Hollmann an Octopus remembered its en- 

 counter with a lobster in a remarkable manner,f while 

 according to Schneider these animals learn to know their 

 keepers.! 



Seeing that memory in various stages of development thus 

 unquestionably occurs among the Mollusca, I thought it worth 

 while to try some experiments in this connection with the 

 Echinodermata, but they all yielded negative results. It has, 

 however, been alleged that if a star-fish be removed from its 

 eggs, it will crawl back again to the place where they were ; 

 and if this statement were confirmed, it would of course 

 prove memory in the Echinodermata. Hitherto I have myself 

 had no opportunity of testing it, and therefore my expe- 

 riments were confined to endeavouring to teach star-fish a 

 few simple lessons, which, as I have already implied, they 

 would not learn. I am more surprised with my failure in 

 this respect with the higher Crustacea ; for although I have 

 tried similar experiments with them, I have never been able 

 to teach them the simplest things. Thus, for instance, I have 

 taken a hermit crab, put it into a tank filled with water, and 

 when he had protruded his head from the shell of the whelk 

 in which he was residing, I gently moved towards him a pair 

 of open scissors, and gave him plenty of time to see the 

 glistening object. Then, slowly including the tip of one of 

 his tentacles between the open blades, I suddenly cut off the 

 tip. Of course the animal immediately drew back into the 

 shell, and remained there for a considerable time. When he 

 again came out I repeated the operation as before, and so on 



* Animal Intelligence, p. 26. f Ibid., p. 27. J Ibid., p. 30. 



