464 



Messrs. F. W. Keeble and F. W. Gamble. 



whilst another runs out into its network of processes. Change of 

 colour appears to be due to a fresh pigmentary deal of the shuffled 

 colour-pack. 



Whether chemical changes play a part in converting one pigment 

 to another or no, we are not yet in a position to say. All the evi- 

 dence we have is against the view that the colour-elements of Hippo- 

 lyte are cells like the chromatophores of the frog. The " muscle-ehro- 

 matophores " bear tubular processes limited by a distinct membrane. 

 The processes of the skin-chromatophores penetrate between the 

 epidermal cells and form networks. The movement of the pigment 

 is not due to a change in the form of the " chromatophore " but to 

 a movement flowing to or from the central part. Further details of 

 these colour-elements are given in our larger paper. 



IV. The Habits of Hippolyte varians. 



Hippolyte lives in swarms amongst the weeds of the seashore. In 

 some places it is most abundant upon the Halidrys and other algae 

 which flourish luxuriantly in the "laminarian" zone, and are only 

 exposed by very low spring-tides. In other places the Zostera-beds 

 and the masses of Fucus form its chief resorts. Each colour-variety is 

 a marvel of protective coloration. Each is to be found among weeds 

 of a closely similar hue and adheres to its chosen habitat -with the 

 greatest tenacity. Though it has the power of making powerful leaps 

 and of swimming, only under the greatest provocation can Hippolyte 

 be induced to take this exercise. At night as well as during the day 

 these prawns are still to be found on their food-plants ; and, should the 

 receding tide lay the weeds bare, the Hippolyte may still be found by 

 shaking them into a net. Should the special food-plants of any given 

 colour-varieties be mixed with other weeds, the prawns will after a 

 time select, each after his kind, the weeds in which it naturally feeds 

 and with which it agrees in colour. Generally speaking, Hippolyte 

 prefers shade to direct sunlight or to artificial light. The emerald 

 green variety found on Zostera, whether at a comparatively high zone 

 on the shore or in the " laminarian " zone, is exposed to a considerable 

 amount of light on account of the "blades" of this grass being- 

 separated from each other and not growing in the shade of deep rock 

 pools. The brown and red varieties of Hippolyte are, on the* other 

 hand, associated with dense masses of weed attached to rocks ; so that 

 the light-intensity in which they live, even at half-tide, is probably 

 lower than that of the beds of Zostera. The bearing of these facts on 

 the changes of colour are referred to in Section VIII. 



Hippolyte exhibits a certain sexual dimorphism both with regard to 

 size and to colour. This may be expressed by saying that the males 

 are on the average much smaller and less elaborately patterned than 



