008 



TONGUES OF GASTEEOPODS. 



Tongue of Doris tuberculata. 



rated. The Tongue of Trochus zizypliinus, represented in 

 Fig. 319, is one of the most beautiful examples of this form; not 



only the large Teeth 

 Fig. 320. of the lateral bands, 



but the delicate leaf- 

 like Teeth of the 

 central portion, having 

 their edges minutely 

 serrated. A yet more 

 complex type, how- 

 ever, is found in the 

 Tongue of Haliotis ; 

 in which there is a 

 central band of Teeth 

 having nearly straight 

 edges instead of points : 

 then, on each side, a 

 lateral band consist- 

 ing of large Teeth 

 shaped like those of 

 the Shark ; and be- 

 yond this, again, 

 another lateral band on either side, composed of several rows of 

 smaller teeth. Very curious differences also present themselves 

 among the different species of the same Genus. Thus in Doris pilosa, 

 the central band is almost entirely wanting, and each lateral band 

 is formed of a single row of very large hooked teeth, set obliquely, 

 like those of the lateral band in Fig. 319 ; whilst in Doris tuber- 

 culata, the central band is the part most developed, and contains 

 a number of rows of conical Teeth, standing almost perpendicu- 

 larly, like those of a harrow (Fig. 320). 



473. Many other varieties might be described, did space permit; 

 but we must be content with adding, that the form and arrange- 

 ment of the Teeth afford characters of great value in classification, 

 as was first pointed-out by Prof. Loven (of Stockholm) in 1847, 

 and has been since very strongly urged by Dr. J. E. Gray, who 

 considers that the structure of the Tongue is one of the best guides 

 to the natural affinities of the Species, Genera, and Families of 

 this group, since any important alteration in the form or position 

 of the Teeth must be accompanied by some corresponding pecu- 

 liarity in the habits and food of the animal.* Hence a systematic 

 examination and delineation of the structm*e and arrangement of 

 these organs, by the aid of the Microscope and Camera Lucida, 

 would be of the greatest service to this department of Natural 

 History. The short thick tube of the Limax and other Terrestrial 

 Gasteropods, appears adapted for the trituration of the food pre- 



* "Annals of Natural History," Ser. 2, Vol. x. (1852), p. 413. 



