BEHAVIOR OF LOWER INVERTEBRATES 375 



Esterly (10) has reported records of the daily depth migra- 

 tions of Calanus finmarchicus. During June and July the great- 

 est assemblage at the surface of the water is between seven and 

 eight P. M. The migration begins before midnight. Its cause, 

 Esterly thinks, is light, but not directly; rather by the effect 

 of light upon geotropism. 



Doubt is cast on the very existence of such depth migrations 

 by Franz in the second of the two papers by him on our list 

 (12). He is strongly inclined to think that biologists have been 

 led to suppose that daily migrations occur from the surface of 

 the water to the deeper regions and vice versa, by the simple 

 fact that in daylight the animals can see and avoid the collect- 

 ing net, whereas at night they cannot. It scarcely seems prob- 

 able that so obvious a source of error as this should have been 

 overlooked. Franz believes that phototropic reactions are never 

 shown under the influence of light alone, but only when unfav- 

 orable life conditions exist, so that the flight-reflex occurs. 

 Y\ hether the phototaxis is positive or negative depends on 

 whether the animal in its ordinary surroundings can escape into 

 the open or into covering. In the first of the two papers on 

 our list (11), he shows that various animals, including copepods 

 and Daphnia, display phototropism only when confined in a 

 small space. In the second paper he makes a similar observa- 

 tion on Palaemon serratus and on some larval Crustacea and 

 worms. Marine copepods show a varying response to light, 

 some individuals being positive, others negative, and the tropism 

 of a given individual is reversed at times. Franz thinks that on 

 being introduced into the observation vessel, most of them trv 

 to escape by swimming towards the light, and that when this 

 procedure is not successful, they become negative. Animals 

 which may display either negative or positive phototropism are 

 those which under normal life conditions can escape in either 

 way. Very young larvae are predominantly positive, owing to 

 their need to seek light. Phototropism being thus dependent on 

 the flight-reflex, "there is scarcely any analogy between photo- 

 taxis in animals and phototropism in plants." A final section 

 of this paper considers the peculiar behavior of Hemimysis, 

 which oscillates back and forth in the water in which it is con- 

 fined, its excursions being from ten to twelve centimeters long. 

 Franz thinks that the turning occurs when the animal gets 



