Literary Notices. 289 



Yerkes, Robert Mearns. Reactions of Daphnia pulex to Light and Heat. 

 Art. XVIII, pp. 359-377- 



The author defines as phototactic "all those reactions in which the 

 direction of movement is determined by an orientation of the organism 

 which is brought about by the light," and as photopathic, those "in 

 which the movement, although due to the stimulation of light, is not 

 definitely directed through the orientation of the organism." "In both 

 intensity of the light, not the direction of the rays, is the determining 

 factor. 



Daphnias were introduced into a flat dish of water illuminated 

 only by a band of light focussed on the bottom and measuring i x 16 

 cm., one end of which was brighter than the other. The animals 

 swim into an intensity of 100 candle-power and remain there, and they 

 do this even when the adiathermal screen is not used, so that they die 

 of heat within a few seconds after reaching the brightest spot. "There 

 is no evidence of an 'optimal' intensity between o and 100 candle- 

 power." The directive influence of light grows no less as the animals 

 progress toward their goal, i. e. there seems to be no "adaptation," 

 nor is there any evidence of fatigue. A sudden change in the inten- 

 sity of the light is a stronger stimulus than a gradual change. The 

 brighter the light the faster the progress of the animals, and this is due 

 not only to the greater precision of orientation but also (contra Daven- 

 port and Cannon) to swifter swimming movements. 



Daphnias are negatively thermotactic at a temperature of 28° C. 

 The thermotactic reaction is elicited by the actual temperature of the 

 water about them, whereas the radiant heat accompanying light has no 

 appreciable influence. The thermotactic "movement is not direct, 

 but irregularly wandering. It is, however, in all probability due to 

 differences in the intensity of stimulation for different regions of the 

 animal's body and is therefore in principle the same as the photopathic 

 reaction," or the phototactic. E. b. h. 



Sargent, Porter Edward. The Torus Longitudinalis of the Teleost Brain ; 

 its Ontogeny, Morphology, Phylogeny and Function. Art. XX, pp. 399- 

 416. 



The interesting longitudinal thickenings of the roof of the mid- 

 brain known as the torus longitudinalis has been the subject of several 

 researches by the above author, whose previous results are here in part 

 summarized and also extended over more forms. A description is 

 given of its variations in certain members of the Siluridae, Cyprinidae, 

 Salmonidae, Amblyopsidae, Gasterosteidae, Atherinidae, Sciaenidae, 



