408 S. J. HOLMES 



In a paper in general ecology of Folliculina Andrews (4) 

 records a number of observations on the behavior of this form. 

 Ordinarily the species lives in tubes secreted by its body, but 

 it often leaves these and swims through the water; it is posi- 

 tively phototactic and thigmotactic, and these traits lead it to 

 settle down upon the younger parts of plants to which it is 

 usually found attached. There is a strong tendency for indi- 

 viduals to aggregate in groups. 



Baunacke (5) has considered various organs which might pos- 

 sibly occasion the orientation of Limax and other mollusks to 

 gravity. He excludes light, tactual, and chemical stimuli and 

 finds that orientation occurs in a medium of the same specific 

 gravity as that of the animals. The statocyst alone is con- 

 sidered to be the organ directly concerned in orientation to 

 gravity. Mollusks from which this organ has been removed 

 are unable to orient themselves to gravity in the normal way. 



The orientation of crustaceans to gravity forms the subject 

 of an extended discussion by Buddenbrock (7) who recognizes 

 three distinct factors which conspire to preserve the normal 

 position of these animals. There is (1) the tendency to present 

 the dorsal surface to the light (Lichtriickenreflex) which the 

 author rinds to be widespread among pelagic crustaceans. Then 

 there is (2) the orienting function of the statocysts, and (3) a 

 general reflex dependent upon no particular organ which leads 

 the animal to keep the ventral surface below. In some crusta- 

 ceans orientation to gravity may persist after the destruction of 

 both statocysts and eyes. 



According to Cowles (8) the starfish Ecinaster spinosus moves 

 toward a white wall and away from a black one. 



Dice (9) has analyzed the factors involved in the vertical 

 migrations of Daphnia pulex. At 20° C. Daphnias are normally 

 positive to weak light but indifferent to light of higher intensity. 

 Increase of temperature makes them less positive, while decrease 

 of temperature makes them more so. Light of high intensity 

 makes Daphnias positively geotactic, while a decrease of light 

 intensity has the reverse effect. These responses help to explain 

 the diurnal movements of these forms. During the day Daph- 

 nias, at least in certain localities, are found more in deeper 

 water while they commonly rise to the surface at night. This 

 migration is due in part to the direct influence of light, but 



