202 journal of Comparative Neurology and Psychology. 



vestigat. rs has demonstrated that the Crustacea are more influ- 

 enced by the directive factor of the hght rays than by the intensity, 

 and, more recently still, Keeble and Gamble (1904), in their 

 excellent work on the color physiology of the higher Crustacea, 

 have shov^'n that the nature of the background may be an impor- 

 tant factor in determining the reaction of many species. 



The Malacostraca have received less attention than have the 

 Entomostraca, and it is only for a comparatively short time that 

 anything has been known concerning the reactions of either the 

 larvae or the ^dults of decapod Crustacea. With the adult forms 

 of the decapods results have been readily obtained. Holmes 

 (1901) found that several species of terrestrial amphipods mani- 

 fest a strong positive phototactic reaction, while all aquatic species 

 are negatively phototactic. We know further from Keeble and 

 Gamble (1904) that the adult form of Palemon is negatively pho- 

 totropic and that Hippolyte is positively phototropic. Hippolyte, 

 according to Keeble and Gamble, not only moves toward the 

 light, but also "prefers" a white to a black background. Macro- 

 mysis inermis reacts positively or negatively in accordance with 

 the character of the background or the nature of the physical 

 environment. It is positively phototropic on a white background, 

 and negatively phototropic on a black background. Further- 

 more, when a choice of background is made possible, Macromysis 

 "selects" the black. In the case of Hippolyte, the larvae respond 

 positively to light, as do the adults. Bell (1906) states that the 

 adult crayfish is "somewhat negatively phototactic" and that 

 difference in the intensity of light made but slight difference in the 

 reactions. Other investigators have show^n that the adults of 

 several species of Crustacea react either positively or negatively 

 to light. Very few investigators, however, have studied system- 

 atically the reactions of Crustacea in the larval stages. Among the 

 first, LoEB (1893) reported the reactions to light of Limulus in the 

 "trilobite stage." These larvae, he said, are at first positive, and 

 later, negative. Pearl (1904), by repeating Loeb's experiments, 

 ascertained that this larval stage of Limulus manifests at first 

 a negative reaction, and that later, a relatively small number of 

 individuals gives a positive reaction. It was learned by Keeble 

 and Gamble (loc. cit.) that the response of the larvae of Palemon 

 is the direct opposite of the reaction of the adults. Bohn (1905) 

 discovered that the larvae of the European lobster (Homarus vul- 



