34^6 LEAVES FROM THE 



these lacertians, and that which governs the appearance 

 and disappearance of coloured spots in the mantles of 

 several of the ce^Dhalopods or cuttles. 



So long ago as July, 1819, Signer Giosud Sangiovanni 

 read to the Royal Academy of Sciences, at Naples, his 

 able and interesting paper, intituled Bescrizione di un 

 particolare Sistema di Organi, e de' Fenomeni ch' esso 

 produce; scoverto ne' Molluschi Cefalopodi, in which 

 he described the structure and properties of the colorific 

 stratum of the skin of the cepJialopoda, upon which the 

 observations of M. Milne Edwards are in a great measure 

 based. Professor Owen quotes it, in his admkable article 

 ' Cephalopoda,' in the Cyclopcudia of Anatomy and 

 Physiology: and, as this part of the organization of those 

 mollusks is the key to the changes of colour in the cha- 

 meleon, those who are interested in the subject may like 

 to see a brief account of the mechanism by which the 

 changes are effected in the marine animals. 



The epidermis of the cephalopods generally forms a 

 thick, white, semi-transparent, elastic, external layer, 

 which is easily detached by maceration. Professor Owen 

 remarks, that the colorific stratum of the integument 

 forms, both in its structure and vital phenomena, one of 

 the most curious and interesting parts of the organization 

 of this singular class of animals, and that the nature of 

 this layer, when thoroughly understood, may be expected 

 to elucidate the mysterious operations of light in produc- 

 ing and affecting the colours of animals. This stratum, 

 which is analogous to the rete miicosum which gives 

 colour, or ' complexion,' as it is termed, to man, consists, 

 he observes, of a very lax and fine vascular and nervous 

 cellular tissue, containing an immense number of small 

 closed vesicles, which vary in relative sizes in different 

 species. These vesicles are of a flattened oval or circular 

 form, and contain a fluid in which a denser colouring 

 matter is suspended. The colour is not always identical 



