their Secretions. 619 



mottled black and white. Mr. Collier says, of some tropical 

 species, that the foot is " blackish red in the Murices gene- 

 rally ; green in AStrombus, and some species of Tr6chus ; 

 black in Bulla ovum ; deep red with faint designs, like those 

 of the shell, in Conus tiilipa, marmoreus, and its varieties ; 

 spotted, in B\xQC\n\\\xiHdrpa\ bright yellow, in ^uccinum Cas- 

 sis ; mottled, in Oliva ; and deep brown, from spots, in some 

 species of Voluta." (Edin.Phil Journ.^ Oct. 1829, p. 228. The 

 names used by Mr. Collier are those of Linnaeus.) The snail 

 of the beautifully marbled harp shell {Hdrpa ventricosa La- 

 marck) glories in a rich vermilion red skin. " In the Mauri- 

 tius, it is the amusement of the place, to watch over the trim 

 apparatus of lines hung over some sand-bank to tempt the 

 various brilliant species of Oliva, which there abound, or to 

 wait for the more rare approach of the harp shell, till the 

 rich hues of its inhabitant are seen glowing through the clear 

 blue water, in the rays of a tropical rising sun." (Broderip, in 

 Zool. Journ., vol. ii. p. 199.) 



The colours of the naked Mollusca are very various : there 

 are black, white, grey, brown, yellow, red, and even green 

 species ; and the colours are sometimes uniform and single, 

 but more commonly mixed, and disposed in freckles or clouds. 

 To dwell, however, on such a subject would be useless ; and 

 I pass on to notice the very curious phenomena 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 differ- 

 ent 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, appear- 

 ing and disappearing with the velocity of lightning : sometimes 

 they are like spots on different parts of the body ; and some- 

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

 These appearances are produced " by the rapid and simul- 

 taneous contraction which takes place in all the vesicles of 

 a particular part of the body, and from the sudden and 

 simultaneous 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. 



