BEHAVIOR OF LOWER INVERTEBRATES 395 



the starfish by sight, since if some of the pulp of a starfish is 

 introduced near a Pecten with a pipette the same precipitate 

 flight is made. Destruction of the abdominal sense organ or 

 the osphradium does not prevent this response. Pecten nor- 

 mally lies on its right side, and if placed on its left side quickly 

 rights itself. Orientation is believed to be controlled by the 

 otocyst, but this was not conclusively proven. 



Most of the observations of Doflein ^^ were made on two 

 species of Leander, although some other decapods w^ere studied. 

 There are many observations and experiments on color changes 

 and reactions to variously colored environments. Studies were 

 made of reactions to touch, chemicals, and light; of the habits 

 of the animals, and the characteristic responses of various parts 

 of the body. 



Various species of Cladocera were found by Ewald ^° to undergo 

 periodic changes of light reactions of only a few minutes dura- 

 tion. Cladocera adapt themselves rather quickly to light of 

 a certain intensity, and after a number of periodic migrations 

 gradually cease to respond. A diminution of light tends to 

 make them positive, while an increase of light induces the nega- 

 tive reaction. All the reactions of the Cladocera to light are 

 attributed to variations in the intensity of light. The daily 

 depth migrations of Cladocera are explained as due, in large 

 part, to changes in the sense of phototajds consequent upon 

 the increase or decrease of light. There is a lengthy discussion 

 of the general subject of orientation. The distinction commonly 

 made between phototaxis and photometry or photopathy is 

 not a valid one, since all reactions to light are considered as 

 reactions either to an increase or a decrease of illumination.- 



There is no evidence, according to the author, that light 

 acts as a constant stimulus. Phototaxis occurs where the 

 reaction to the stimulus happens to be an orienting one. Posi- 

 tive or negative reactions depend upon whether the animal 

 is more stimulated by a decrease or by an increase in the 

 intensity of light. 



Franz " claims that phototaxis in many cases is a laboratory 



product, being often the result of confinement within a small 



space. The positive reaction is observed commonly in forms 



which often find a means of escape by going towards large 



. lighted areas. Reaction to light in most higher forms is adaptive. 



