468 



The Colour- Physiology of Hippolyte varians. 



the nervous mechanism of the change, but the histological examina- 

 tion of these experiments is not yet complete. 



IX. The Role of the Eye and Nervous System. 



Removal of one eye produces no effect on the body-colour. Removal 

 of both, either produces no effect or a rapid nocturning. The animal 

 is plunged in night. Under such circumstances the periodic habit may 

 re-assert itself and a recovery with subsequent fairly punctual nocturn- 

 ing take place. The chromatophores of detached limbs, and in the 

 bodies of blinded specimens, exhibit alterations of their pigments — 

 Avhen subjected to different light-stimuli, quite similar to those which 

 occur in the. intact animal under the same conditions. Therefore (1) 

 an intrinsic rhythmic nervous change supervises the periodic change in 

 the pigments ; (2) the eye is the most important auxiliary in modifying 

 nervous control ; (3) local government plays a part. In variegated 

 colour-forms, which show, as in a mirror, the pattern of their weed, it 

 can scarcely be doubted that both central and local government 

 co-operate, and so produce a result of such consummate delicacy. 

 Here there is expansion of one pigment, here of another, there com 

 plete contraction. The light acting through the eye on the central 

 nervous system cannot be supposed to differentiate itself into such 

 diverse stimuli as are required to produce the colour- variety. Local 

 control under a strong central organisation seems to be the only likely 

 force and the evidence favours this view. 



X. "Chromatophores" of la real form*. 



We have succeeded in hatching out the zoese of Hippolyte carta us and 

 in following their development for a short time. Several of the colour- 

 elements acquire their pigment before the time of hatching. There are 

 two pigments, one red and the other yellow by reflected and dull green 

 by transmitted light. A few chromatophores contain red only. All the 

 colour-elements are distributed symmetrically. They occur in the 

 neighbourhood of the eyes, the liver, and at the sides of the abdominal 

 segments. 



In the zoea the pigments react with astonishing rapidity to certain 

 changes of light-intensity. A bright light brings about very rapid 

 contraction, while a dark background effects expansion of the yellow- 

 green and more slowly a similar change in the red. A diffuse blue 

 substance was noticed frequently as though exuding from the dense red 

 body of some " chromatophores." This may be the result of a 

 destructive action of light upon one or both of the pigments, and 

 should this be so, we may find in a study of the larval stage the 

 meaning of the blue colour of Nocturnes. 



