726 COMPARATIVE AND GENETIC PSYCHOLOGY 



starfish, but he reaches this conclusion from the disputed stand- 

 point of the continuity hypothesis. "The starfish," he says, "per- 

 ceived the proximity of food, as shown by their immediately crawling 

 towards it." 1 He thus argues consciousness from simple reaction, 

 instead of experimenting on the starfish to discover if they would 

 riot react similarly to unodorous stimuli. Other experiments on 

 different orders of radiates have not to my knowledge resulted in 

 the discovery that they make adaptive reactions, though Loeb's 

 experiments offer evidence of their discriminate movements. 2 

 The tentacles of actinians, for example, draw in meat, and reject 

 paper; but so far as is reported, they do not handle the meat or 

 paper with increasing expertness. 



Studies of mollusks, also, so far as I know them, have consisted in 

 examination of their sense-organs, 3 in the study of the function of 

 their nerve-systems, and in experimental observation of their imme- 

 diate reactions, but have not included any effort to train them to 

 adaptive reactions. None the less, Loeb concludes that cephalopods 

 may possess associative memory. 4 It is certainly to be wished that 

 some investigator might, study different orders of the radiates and 

 the mollusks, with the express aim of discovering whether they may 

 be trained to adaptive reactions. For herein, and not in the posses- 

 sion of acute sense-organs nor in the capacity for discriminated yet- 

 invariable reactions, is the trustworthy test of consciousness. 



Different orders of the articulates have been studied with this 

 special end in view, with the result that they have been trained 

 to simple motor habits. Loeb, to be sure, interprets the movements 

 of worms as mere reflexes, but he argues mainly from the inconclu- 

 sive premise that their most complex reactions seem not to require 

 coordination through brain-centres. Yerkes, 5 Yerkes and Huggins, 8 

 and Spaulding 7 have experimented on Crustacea and have proved 

 that both crayfish and crabs can learn by the trial and error method 

 to find their way through simple labyrinths. Spaulding's experi- 

 ments are noteworthy, since he trained his crabs to a habit opposed 

 to their instinctive heliotropism, namely, to seek food in the dark. 8 



1 Jelly-fish, Star-fish and Sea-urchins, p. 321. 

 z Loeb, op. cit., chap, iv, pp. 50 seq. 



3 Cf. J. W. Spengel, Die Geruchsorgane u. das N ervensystem der Mollusken 

 Zeitschr. f. uriss. Zool., xxxv, p. 333; W. A. Nagel, Bibliotheca Zoologica, Heft 

 18, 1894; Loeb, Der Heliotropismus der Thiere; J. Steiner, Die Functionen d. 

 Central Nerven Systems der wirbellosen Thiere, Sitzungberichte d. Akad. d. 

 Wissensch. i, p. 32, zu Berlin, 1890. 



4 Loeb, op. cit., p. 227. 5 Biological Bulletin, m, 5, Oct. 1902. 

 8 Harvard Psychological Studies, I, pp. 565 seq., 1903. 



7 Journal of Comparative Neurology and Psychology, 1904, vol. iv, pp. 49 seq., 

 esp. p. 58. 



8 The opposed results of Bethe's experiments on crabs (Archiv fur mikroscop. 

 Anatomic, LI, p. 447, 1898, quoted by Yerkes, Harvard Psychol. Studies, I, 

 p. 565) are evidently due mainly to the insufficient number of his experiments 

 (five or six). 



