1182 Journal of Applied Microscopy 



GENERAL PHYSIOLOGY. 



Raymond Pearl. 



Books and papers for review should be sent to Raymond Pearl, Zoological 

 Laboratory, University of Michigan, Ann Arbor, Mich. 



Gamble, F. W., and Keeble, F. W, Hippolyte This paper deals with the color changes 



Scfsd. N%"% i^S-e," p'r/^e. P,i ^h°«" by 'he prawn Hippolyte varians, 



which lives in shallow water clinging to 

 seaweeds and zoophytes, in relation to different environmental conditions and 

 to stimulation by light. It has been often noted that Hippolyte shows a 

 very remarkable similarity in its coloration to its surroundings, and it was the 

 purpose of the authors^to determine under exact experimental conditions 

 what the nature of these adaptive color changes was, and how they were brought 

 about. As an introduction a description is given of the different natural varieties 

 of this prawn and of the condition of the chromatophores associated with these 

 varieties. Uniform brown, pink, red, and green adult specimens were collected, 

 while among immature individuals "red liners," "black liners," "green liners " 

 and jellow barred specimens were common. The " liners " are animals which 

 are transversely striped with the color indicated. The pigments are contained in 

 chromatophores which lie under the epidermis in the connective tissue and 

 muscles and about the alimentary canal and blood vessels. The chromatophore 

 itself consists of a central body from which diverge a number of line, ramifying, 

 hollow tubes. In these tubes and the central body are contained the pigments 

 which give the color to the animal. There are three pigments, red, yellow and 

 blue, and color changes are caused by the movement of these pigments in the 

 tubes. There is a layer of chromatophores in the connective tissue just beneath 

 the epidermis, the processes of which form a close meshwork about the clear 

 transparent cells of the epidermis itself. To the combination of the three 

 pigments in this epidermal meshwork is due the color of the animal as a whole. 

 For example, in a green prawn the tubes of the meshwork are found to contain 

 both yellow and blue pigment side by side. 



The animal exhibits three sorts of color changes: (a) slow, sympathetic 

 changes of color accompanying changes in the color of the weed to which the 

 individual is attached ; (b) rapid color changes caused by changes in light 

 intensity ; (c) periodic nocturnal color changes, (a) In regard to adaptive color 

 changes in response to changes of the weeds, it was found that the animals were 

 capable of only very slow sympathetic changes. The adaptations observed in 

 nature are the result of the selection by the animal of those weeds whose color 

 most closely matches their own. (b) The intensity of illumination has a pro- 

 nounced effect on the color of the animals and this effect is produced in a very 

 short time. In high light, or in low light scattered evenly from the surface of 

 the containing dish, there is a retraction of the red pigment and an evolution of 

 the blue and the yellow, producing a green coloration of the animal ; while in low 

 light absorbed by the walls of the vessel the red remains expanded. The color 

 quality of the light has no effect on the color of the animal provided the 



