HAVE FISHES MEMOKY. 389 



new animal is formed in miniature, lacking- the mouth cavity. If food 

 be laid upon the tentacles so produced, they contract again and again 

 to the point of fatigue, but they can not press it into the body. The 

 act, then, is accomplished, in these low organisms, by an apparatus 

 present from the first, and put into efficient motion by the proper 

 stimuli. Hig-h up in the ranks of animal life the act of mere swal- 

 lowing is executed by means of a bit of mechanism operating- with 

 unvarying- regularity. Human beings may take or refuse to take 

 food, l)ut as soon as a bite passes the arch of the palate and enters the 

 domain of the swallowing apparatus, properly speaking, it is beyond 

 their control. It is then caught up and pushed along by a series of 

 pharyngeal movements that may occur in individuals bereft of all con- 

 sciousness. The sea-anemone, an illustration that might easily be 

 multiplied, proves that an irritation is needed to induce the act of 

 eating. The sort of movements brought about by means of closely 

 connected, long'-plowed paths of sensation and motion,, and always 

 capable of being called forth by the same irritation in the identical 

 way; such movements are called combined reflexes. To cause them, 

 the first condition is an irritation of the proper kind, but the irritation 

 must furthermore be of a certain degree of strength, which in turn 

 can be attained by the short application of a forcible stimulus or the 

 long-enduring application of a Aveak stimulus. We saw above that in 

 the higher animals the act of eating divides itself into two parts — deg- 

 lutition is automatic, but for the seizing of food other stimuli, appar- 

 ently dependent upon the will, must be called into action, 



A striking example is available to show that the first division of the 

 act of eating also occurs only in response to a stimulus of a certain 

 degree of intensity. During the day a frog is a rather inert animal. 

 He spends most daylight hours quietly, in a sort of doze. He is pecu- 

 liarly fitted to serve the purposes of this demonstration, because often 

 long intervals elapse during the day between his times of taking food. 

 We have numerous descriptions of how the frog eats — how the "sly 

 robber" eyes his boot}^, how he sits quietly for a long time before he 

 seizes the "enemy lulled into security by his immobility," etc., how 

 he executes many deeds of crafty cunning. Simple observation teaches 

 otherwise. An earthworm crawls in front of a frog. Unless he is 

 very hungry this simple optical irritation does not suffice to induce 

 him to spring upon his prey and seize it. Now, the worm moves on, 

 the optical stimulus gathers force, and finally it calls forth the first 

 reflex act— the frog turns his head toward the worm. He is not yet 

 ready to spring, but the longer the impression of the crawling worm 

 acts upon him the more restless grows the frog, and at last he jumps 

 forward with a bound, often enough missing his prey. What he has 

 done so far must be classified wholly under well-known laws of reflex 

 action. There is nothing to suggest greed of booty or cunning; all 



