234 Journal of Comparative Neurology aud Psychology. 



state of the surface of a shell, certain elements of its external form (degree of 

 curvature, line of greatest slope etc.) and of its interior form (degree and 

 direction of curvature, etc.), its dimensions, especially the interior dimension, and 

 its weight." 



Just such detailed studies of the behavior of an animal, as the author has given 

 us for the hermit crab, are of inestimable value for the furtherance of the science 

 of organic activities, for they furnish the facts which enable us to undertake 

 classification and generalization. 



The papers of the second group I shall review only by title, in order to devote 

 all available space to those of the third and fourth groups. 



BoHN has done good service to his science in showing (No. 5, p. 2, et seq.), by 

 an analysis of conditions which influence the movements of Convoluta, that 

 stimulating factors must be studied in their relations to one another, and that at 

 the same time, account must be taken of the physiological state of the organism, 

 and of the conditions which have previously influenced its activities. As the 

 author puts it, there are causes actuelles et causes passees, neither of which can be 

 understood in its relations to the behavior of the animal without knowledge of 

 the other. In Convoluta, for example, reactions to gravity change with sun and 

 tide. As the tide rises the worm becomes positively geotropic and burrows into 

 the sand thus finding protection from the waves. As the tide falls the reaction to 

 gravity changes to negative and the worm comes to the surface of the sand to 

 feed. This regular change in the sense of the response to gravity (surely we should 

 not call it a response to gravity) has become habitual and persists even when the ani- 

 mal is placed beyond the reach of sun and tide. 



Since it is impossible to state even the general results of all thd author's in- 

 vestigations, I choose for special attention the memoir (No. 28), in which he 

 has brought together the chief results of many of his briefer papers. It deals 

 especially with the reactions of the molluscs, Littorina rudis, L. littorea and L. 

 obtusata, and the annelid, Hedista diversicolor, to light and with the influence of 

 other environmental factors on these reactions. To indicate the general nature 

 of the author's studies with these animals, I quote the following translation of a 

 portion of paper No. 25, which is in a sense a summary of the contents of the 

 memoir. '^ 



"Upon the Boulogne coast, at the foot of dismantled rocks or dunes, there are 

 found some large calcareous blocks which are reached by the sea only every five 

 hours, during high tide; in the fissures and crevices which they present are lodged 

 a multitude of small Littorinas (L. rudis). When the blocks are dry, during the 

 periods of low water, these molluscs are retracted into their shells; during high tide 

 under the influence of the beating of the waves, they emerge from their torpor and 

 begin to wander over the wet rocks. 



"If they are placed upon the sand, several meters from the rocks, the following 

 curious facts may be observed: instead of moving in the direction of the sun's 

 rays, in accordance with the classical theory of phototropism, the Littorinas move 

 toward the rocks which are situated at a relatively aonsiderable distance, and it is 

 to the highest rock that all the paths lead. Leaving out of account irregularities 

 in the surface of the ground, these paths are from the beginning parallel with one 

 another, and perpendicular to the sombre vertical wall of rocks. In the vicinity 



