590 F. W. GAMBLE AND F. W. KEEBLE. 



the sea-sliore or by trawling in the " Laminarian zone." 

 Whilst specimens so obtained may present colours ranging 

 through the whole gamut of the spectrum, many exhibit an 

 astonishingly close resemblance to the colour of the weeds, 

 zoophytes, or other objects to which they obstinately cling. 

 Attracted by this phenomenon of " protective resemblance," 

 naturalists, who have desired to record its features, have 

 observed that the prawns change colour in a very short time : 

 that an emerald green or rich brown colour may lose much 

 of its brilliancy or even its characteristic tone within the time 

 elapsing between capture and subsequent examination in the 

 laboratory. The trivial name varians has thus come to 

 connote not merely that the colour of these prawns exhibits 

 great individual differences in tint and pattern, but that, in 

 addition, the colour of the same individual may alter. It is 

 but a step further to the idea that all the different colour 

 varieties may be capable of passing into one another — a 

 possibility often expressed but never experimentally verified. 

 The bare fact of colour-change among Crustacea appears 

 to have first been observed and recorded by Kroyer (1842) 

 in this very species Hippolyte varians, or, as he called it, 

 H. smaragdina. "In this species," he says, "I have ob- 

 served a very remarkable colour-change. The usual emerald 

 green colour of those specimens which I have placed with sea 

 water in a glass vessel passed rapidly into an olive or into a 

 bluish-green colour. The azure spots behind the anterior 

 edge of the carapace became so indistinct that did I not 

 know their position I should have overlooked them. The 

 longitudinal stripe on the carapace changed from blue to 

 yellow, and finally disappeared completely. I believe I have 

 noticed similar changes in other species of this genus, but 

 none so plain or so striking" (1842, p. 244). Other natu- 

 ralists have noticed the same kind of change in this and other 

 Crustacea. Fritz Miiller, for example (1880-81), showed 

 that fresh-water prawns (Atyoida potimirum, Paleemon 

 potiporanga) of South America, when taken from their 

 habitat and placed in a glass vessel, rapidly lose their brown 



