STICKLE-BACKS. 101 



men to a vessel of water, along with an eel of three 

 inches in length, and it speedily attacked and swal- 

 lowed its companion head foremost, but, owing to 

 its great comparative bulk, only partially, the tail 

 remaining suspended from the mouth, so that it 

 was at last obliged to disgorge its prey, though half 

 digested. " The effect of the passions on the colour 

 of the skin in the species of the genus Gasterosteus 

 is remarkable, and the specimen now spoken of, 

 under the influence of terror, from a dark olive 

 with golden sides, changed to pale for eighteen 

 hours, when it as suddenly regained its former 

 tints." 11 * We know not whether, when the latter 

 change occurred, the fish was placed in a vessel of 

 a different colour, but the former alteration may 

 probably be accounted for on a principle well known 

 to naturalists, in accordance with which an almost 

 instantaneous change takes place in the colour of a 

 fish when it either moves spontaneously between 

 two beds of differently coloured ground or gravel, 

 or is transferred from its native haunts to any 

 earthen vessel. Dr. Stark has well shewn that 

 these changes are effected in connection not only 

 with the colour of the inside coating of the vessel, 

 but with the intensity of light to which they may 

 be otherwise exposed. Whatever the physical cause 

 of this may be, the final effect is alike admirable and 

 obvious, in securing them from too inquisitorial ob- 

 servation in shallow rivers, or on sandy shores. 



* Couch's MS. as quoted by Mr. Yarrell, BRITISH FISHES, i. 89. 

 We may add, on the authority of Dr. Johnston of Berwick, that this 

 is one of the few fishes which makes a nest. 



