Yerkes, Animal Behavior. 233 



numbered i, 3, 6 and 7 belong to this group. (3). Studies of the reactions of 

 organisms in relation to light, moisture, gravity etc., and of theories of the 

 tropisms. In this group we may mention numbers 4, 5, 8, 9, 10, 13, 16, 17, 18, 

 19, 20, 21, 22, 23, 25, 26, 27, 29 and 30. (4). Studies which deal with the 

 problems of all the preceding groups. Numbers 28 and 31 are of this nature. 



Concerning the work described in the papers of the first group, it may be said, 

 that were the author to restate his results, there is every reason to believe that hfe 

 would use objective terms almost exclusively, and that the papers would therefore 

 fall into one of the other groups. In other words, what formerly interested him 

 because of its probable psychological significance, Bohn is now concerned with, 

 because of its value as fact. In the introductory chapter of his memoir on re- 

 actions to light (No. 28) he makes clear his present position with reference to the 

 use of subjective terms, and at the same time states his purposes of research. He 

 claims that there is a diflPerence between seeing (a subjective term) and being in- 

 fluenced by light, and that we are not justified in using the word see (voir) in 

 connection with the reactions of certain molluscs, since it involves an interpreta- 

 tion of the phenomena observed, which may possibly be false and which is un- 

 necessary. And he continues, (No. 28, p. 5,) "in this memoir, I shall describe the 

 facts without explaining them, and I shall guard myself well against saying that 

 in Littorina, states of consciousness do not exist and do not intervene. I do not 

 know; I affirm nothing, deny nothing." BoHN does not, however, in any of his 

 papers go to the absurd length of trying to avoid entirely subjective terms. The 

 final result of the introductory chapter referred to above in which the author dis- 

 cusses the dangers to biology of anthropomorphism, psychologic, vitalistic and 

 mechanistic errors, is well summed up in his statement of what he has attempted 

 to do in the memo r (No. 28, p. 14). "(i) To limit mvself to the descriptions 

 of the animal's reactions. (2) To state precisely, as far as possible, the condi- 

 tions of the expeiiments, in taking account of variations of internal conditions 

 as well as of external; of past influences (causes passees), as well as of present 

 influences {causes actuelles). (3) To avoid idealization of the facts, anthro- 

 pomorphism, psychology and philosophy. (4) To employ purely objective 

 language. (5) Not to liken an animal to an inanimate machine. (6) Not to 

 generalise for all animals. (7) To separate clearly the interp''"etation of the 

 facts from the exposition of these facts, and in this domain" to admit only 

 hypotheses easy of verification." 



Of the papers in the first group, No. 12 is worthy of special attention. In it 

 the author describes his studies of the social relations, receptive capacity and 

 modifiability of reaction in the hermit crab. There is an important list of papers 

 which deal with the relations of the crabs among themselves and with other 

 animals, and in addition, valuable historical and critical notes. Bohn 's original 

 observations concern: (l) The nature of the locomotor and prehensile movements 

 of the animals; (2) their perception of the nature of surfaces of diff'erent forms 

 (flat, convex, concave); (3) their perception of the dimensions of a body or 

 cavity; (4) their perception of the weight of a body. The general results of the 

 large number of observations, which were made under natural and experimental 

 conditions, are indicated in the following (No. 12, p. 626): "Eupagurus 

 bernhardus is capable of perceiving by various means (touch, position, trial), the 



