BEHAVIOR OF THE LOWER INVERTEBRATES 409 



more to the effect of light upon geotaxis. Temperature also is 

 a factor, as Daphnias tend to become positively geotactic in 

 high temperatures and negatively geotactic in low. This has 

 a marked influence in the seasonal migration of these animals. 

 Other minor factors of migration are discussed, such as age 

 and wave action. There is no diurnal rhythm independent of 

 the direct action of orienting agencies. 



Ewald (10) finds that Daphnia has two distinct modes of 

 reaction to the light, the orienting response and a response to 

 change in light intensity. By subjecting Daphnias to inter- 

 mittent light Ewald found that the orienting response was not 

 effected by the frequency of interruption, provided that the 

 same amount of light was received in a given time. For the 

 shock reaction, interrupted light affords a much more effective 

 stimulus. Both types of response harmonize with the Bunsen- 

 Roscoe law. Daphnias respond to different colors, and not 

 only to light intensity. 



Fasten (11), in an account of fertilization in a species of cope- 

 pods, describes the copulatory activities of the male. 



Galiano (12) has described, without indicating any general 

 conclusions or discussing his results, a number of experiments 

 on the chemotaxis of Paramecium. Reagents were used similar 

 to those which Paramecium encounters under natural conditions, 

 i.e., culture fluids, distilled water, and dilute alkaline solutions. 



Herwerden (13) placed Daphnias in a horizontal glass vessel 

 one end of which was closed by quartz. When ultra-violet 

 light was passed through the quartz into the water the Daph- 

 nias became negative; when a piece of glass was interposed the 

 reaction was discontinued. In specimens in which the eye was 

 destroyed there was no negative reaction. 



Hess (16) finds that the ambulacral feet of the starfish Astro- 

 pecten retract under the influence of light. If only a small 

 extent of the ventral surface of one ray is illuminated the feet 

 struck by the light rays retract while the others are extended. 

 The oral tentacles of Holothoria show a similar reaction. In 

 both cases red light has little effect but blue and green readily 

 evoke the response. Serpulas (14) react to change in light 

 intensity like color-blind people, i.e., without regard to wave 

 lengths of differently colored lights. Balanus reacts in similar 

 way, ceasing its movements upon a diminution of the light. 



