their Food and Digestive Organs. 



75 



Fig. 5. : a, The tongue, natural size, of the common limpet (Patella vulgata) ; b, a portion magni- 

 fied j c c c, the cartilaginous jaws. — Fig. 6., Jaws of Tritbnia. 



given of it convey not the slightest idea of the extreme beauty 

 and delicate organisation of this wonderful organ ; nor am I 

 able to supply this deficiency. It is sometimes broader than 

 long, as in Tritonia and Doris; at other times elliptical or 

 spoon-shaped, as in the snails ; and in others it is lengthened out 

 in the most extraordinary manner, so as not merely to equal, 

 but greatly to exceed, the length of the body ! * In the latter 

 cases it lies reversed along the gullet, and reaches the interior 

 of the stomach, where it is convoluted or twisted into spiral 

 bendings, like a serpent closely rolled together. The peri- 

 winkles (Littorina) and limpets afford familiar examples of 

 this remarkable modification ; and I enclose a figure of it 

 {Jig. 5. a), from the common limpet : it is a narrow riband- 

 like body, fully 3 in. long, of nearly equal breadth throughout, 

 except at the apex, where it is soft and somewhat dilated, the 

 surface roughened with three rows of teeth, the side rows 

 alternating with the middle one, which is quadrifid, while the 

 side teeth are divided only into two points. There is also 

 placed along each side a double row of cylindrical tubes 

 whose apertures look towards the base. This curious spini- 

 gerous tongue is never protruded beyond the margin of the 

 lips. It seems to be used for rasping down the food ; and, in 

 proportion as the anterior prickles are worn away in this 

 operation and absorbed, another portion of the tongue is 



want of lingual spines. {Phil, of Zoology, ii. 451.) I will not contradict 

 such an observer as Cuvier, although, from my own examination of the 

 organ in question, I had come to a contrary conclusion. 



* For a rude and unfinished figure of the tongue of Tritdnia, see 

 Cuvier's Mem., tab. 2. fig. 8, 9. ; of Aplysia, tab. 2. fig. 6. b ; of Palu- 

 dina, tab. i. fig. 8, 9. ; of Patella, tab. 2. fig. 18, 19. 



