620 Natural History of Molluscmis A7iimals : — 



Even long after death, these vesicles may be made to exhibit 

 •the same alternate contractions and expansions, on the appli- 

 cation of slight irritations. 



NaturalivSts have been long acquainted in some degree with 

 these singular phenomena. Pliny tells us that the cuttlefish 

 change their colour through fear (Hist. Nat., lib. ix. cap. 46.) ; 

 adapting it, cameleon-like, to that of the place they are in. 

 None of the older authors, however, attempted to investigate 

 their cause ; but, of late, several theories have been offered, 

 and two of these are founded on a minute enquiry into the 

 structure of the vesicles. Cuvier said, conjecturally, that the 

 appearances were dependent on the effusion of a coloured 

 jQuid in the areolar tissue of the skin ; and Professor Grant 

 refined upon this hypothesis, by supposing the fluid to pass 

 repeated 1}^ to and from the minute vesicles (Edin, New Phil, 

 Jouni., vol. xvi. p. 3 1 3.) : but this conjecture has been fully dis- 

 proved ; for the spots have no connection with any vascular 

 system, nor do the vesicles contain any encysted fluid. Dr. 

 G. San Giovanni of Naples, an intelligent comparative ana- 

 tomist, offered another explanation, founded on a connection 

 between the vesicles and the nervous system, which he ima- 

 gined he had traced. The colour is correctly stated to be 

 inherent in the tissue itself; and its changes are attributed to 

 the particular structure of the vesicles, each of which, he 

 says, has a circular aperture that opens and shuts, probably 

 by means of a circular muscle, the actions of which are regu- 

 Jated by the will of the animal, through the medium of the 

 nerves, with which the vesicles are connected by means of 

 delicate filaments, scarcely discernible even with the aid of a 

 microscope. But the observations of Dr. Coldstream, one of 

 the most promising among the rising race of naturalists, de- 

 stroy this ingenious and plausible theory. Dr. Coldstream 

 could not discover, by the most careful microscopic examin- 

 ation, the slightest trace of any nervous threads in connection 

 with the vesicles ; and he proved, which seems incompatible 

 with their dependence on the nerves, that the vesicles pos- 

 sessed motion in pieces of the mucous coat which had been 

 removed entirely from the body: nor could he succeed in 

 discovering any opening in them, such as San Giovanni asserts 

 they have, even during their greatest dilatation, and under the 

 most favourable circumstances. " That I might ascertain," 

 to use Dr. Coldstream's own words, " whether or not the 

 motions of the spots were now (after apparent death had 

 taken place) carried on by the influence of external agents, 

 independently of any nervous power emanating from the 

 animal itself, I cut, from a part of the mantle where the 



