COLOUR OF CEPHALOPODA. 235 



or clouds. Cranchia bonnellii affords probably the most 

 remarkable example of colouring in the class. This bizarre 

 Cephalopod, whose form involuntarily reminds us of those 

 fantastic beings with which the genius of Callot has peopled 

 hell, and which the opera sometimes imitates in its marvel- 

 lous scenery, appears to rival the butterflies of tropical suns 

 in gaudiness and brilliancy. A broad membrane unites its 

 six upper arms into a large veil of a very rich purple colour, 

 adorned with six double rows of buttons of sapphire-stone 

 formed by the cups or suckers. The ventral surface of the 

 sac, of the head, and of the two inferior arms, is studded 

 with yellow spots arranged in quincunx, and near each spot 

 there is another, in relief, of blue. These yellow and blue 

 spots lie on a reddish ground sprinkled with purple dots, 

 and have such a lustre in the living animal that they re- 

 semble as many topazes, near each of which a sapphire has 

 been mounted.* To dwell, however, on this subject would 

 be useless ; and I pass on to notice the very curious phe- 

 nomena exhibited in the coloured spots of the Cephalopoda. 

 The surface of these remarkable creatures, particularly 

 the back and sides, is speckled with numberless minute 

 coloured dots, which vary in size, tint, and arrangement, 

 in the different species ; and in the same species are liable 

 to change, in the same respects, according to their degree 

 of developement. These dots are properly follicles, or little 

 bladders, seated in the mucous web (rete mucosum), and 

 consequently covered by the epidermis, which is smooth 

 and transparent. " During life, when the animal is in a 

 state of repose, the vesicles are contracted, and are not 

 visible. When it is excited, by being touched with the 

 hand, or otherwise irritated, the coloured vesicles show 

 themselves and are instantly in motion, appearing and dis- 

 appearing with the velocity of lightning : sometimes they 

 are like spots on different parts of the body ; and sometimes 

 like waves, which rapidly move across its surface." These 

 appearances are produced " by the rapid and simultaneous 

 contraction which takes place in all the vesicles of a par- 

 ticular part of the body, and from the sudden and simul- 

 taneous expansion of all the vesicles on another part ; " but 

 the process may go on until the whole body is covered, and 

 its natural colour become changed for that of the vesicles. 

 Even long after death these vesicles may be made to exhibit 

 the same alternate contractions and expansions on the appli- 

 cation of slight irritation. 



* Ann. ties Sc. Nat. n. s. iii. 344. 



