VI. Biology. 4. Transforming Effects of Environment. 67 



canaries by feeding them with cayenne pepper. Pigeons fed on meat 

 iiave the gizzard modified like that of a bird of prey (thin-walled), 

 whilst, conversely, the stomach of an ordinary flesh-eating bird (G-uU) 

 is so modified by a diet of corn that it becomes like that of a grain- 

 eating bird. 



Interesting experiments have been made upon the transforming 

 influence of an alteration in salinity. A Crustacean living in 

 salt lakes, Artemia salina, nearly related to the fresh water Bran- 

 chipus, is modified, by gradual increase in salinity, into another 

 form, which has been described as a peculiar and different species, 

 A. milhausenii. The modification does not arise immediately in one 

 and the same individual ; it is gradual, extending through many 

 generations. Conversely if A. milhausenii is placed in slightly salt 

 water it becomes A. salina. Further, if the water is freshened by 

 degrees, until it is finally quite fresh, A. salina is gradually modified 

 in the other direction, so that at last it assumes the characters of the 

 genus BrancMpus. 



Animals may also be affected by variations in light; the cave 

 form Proteus, whitish under normal conditions, becomes speckled or 

 brownish if exposed to the light; for the pigment, usually absent, 

 now develops in the skin. If Sticklebacks are put in a glass with 

 a white bottom, they turn quite pale in the course of a few days, 

 and if they are kept five or six weeks under these conditions, the 

 dark colour does not return, even when they are put in a glass with 

 a dark ground.* Similar observations have been made upon other 

 fish. It has been found in not a few species of Butterflies, that the 

 colour of the pupa really depends upon the colour of the background 

 upon which the larva rests during the days immediately preceding 

 pupation. If the larva has lived on a light background {e.g. a light 

 wall), the pupa will be light, and vice-versa. In this, as in the other 

 cases mentioned, the action of light upon the skin of the animal 

 is evidently the primary cause. 



Among Butterflies, noteworthy observations have also been made 

 as to the influence of temperature. If certain pupee are kept at 

 a low temperature, the colour of the Butterfly varies from the normal. 



The seasonal dimorpliism already mentioned, is probably originally 

 called forth, by the effect of a different temperatvire upon the pupse : and as a 

 matter of fact, when the summer pupse ai-e exposed to a lower tempei-ature, 

 specimens may appear which are like the winter-brood. 



In many cases animals are curiously affected by settling in a 

 new locality, no further cause being ascertainable. A few 

 examples will illustrate this. In 1870, a few wild Turkeys were 



* The change depends upon the fact that the pigment-cells (ohromatophores) of 

 the skin have almost entirely atrophied. This definite change in the colour of the 

 skin must not be confused with the colour change occurring in many animals 

 (Cephalopoda, Chameleon), which depends on the alternate contraction and relaxation 

 of the ohromatophores. 



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