6^24- Natural History of Molluscous Animals : — 



The excretion which approaches apparently nearest to this 

 in its character is that of the lanthinae ; but I am not aware 

 that any analysis has been made of it. Planorbis corneus 

 {Jrg. 108.), also, when irritated by any means, or, as Wallis 

 IQQ translates a passage from Lister, by " an 



injection of a grain of salt, pepper, or ginger, 

 into its mouth," pours forth a purple fluid 

 from the sides, between the fork and margin 

 of the cloak ; but the colour is of so fugi- 

 tive a nature, that no acid or astringent has 

 hitherto been found sufficient to preserve the 

 elegancy of its tint, and from turning to an 

 unpleasant rusty hue.* In this respect it agrees with the liquor 

 discharged by Scalaria clathrus, of which Montagu has given 

 us an interesting history. " The purple juice," he tells us, 

 " may be collected either from the recent or dried animal, by 

 opening the part behind the head ; and as much can be pro- 

 cured from five individuals, as is sufficient, when mixed with 

 a few drops of spring water, to cover half a sheet of paper." 

 Neither volatile nor fixed alkali materially affects it ; mineral 

 acids turn it to a bluish green, or sea-green ; sulphuric acid 

 renders it a shade more inclining to blue; vegetable acids 

 probably do not affect it, since cream of tartar did not in the 

 least alter it. These colours, laid on paper, were very bright, 

 and appeared for some months unchanged by the action of 

 the air, or the sun ; but, being exposed, for a whole summer, 

 to the solar rays, in a south window, they almost vanished. 

 The application of alkali to the acidulated colour always re- 

 stored it to its primitive state, and it was as readily changed 

 again by mineral acid : in this particular it differs materially 

 from the succus of J5uccinum lapillus, which, as we have 

 before remarked, is unalterable." (Mont., Test. Brit. Sup., 

 p. 122.) 



It is from the difference pointed out, in the latter part of 

 the sentence just quoted, between the fluid of Scalaria (and, 

 I may add, of lanthina and Aplysia), and the ^uccinum or 

 Purpuriferae, and because it is from the first of a purple co- 

 lour, that I cannot agree with Colonel Montagu, and many 

 other naturalists of eminence, in their opinion, of its having 

 formed any part of the Tyrian dye; for unchangeableness was 

 one of the characters that enhanced the value of the latter; 

 and Aristotle and Pliny state expressly that the colour of that 

 fluid, on its first discharge from the animal, was white. Such 

 a coloured liquor can be procured, as these authors say it 



* Wallis, Nat. Hist. Nori/i., vol. i. p. 371. Lister, in his Atmi. Ang., 

 p. 144., gives a full and very good account of this liquor. 



