258 THE ANIMAL KINGDOM. 



mantle, which is muscular, and capable of alternate con- 

 traction and expansion; they 

 breathe by means of lungs on 

 their back beneath the shell, 

 and to which there is an 

 opening in their side. What 



^ usuallycalled the horns are 



four in number, two short and 



two long ; they are tentaculae, but what is peculiar in 

 them is the circumstance of having the eyes placed at 

 their ends. These Mollusca have a sort of valve, which, 

 when they retire into the shell, closes it like a lid ; it is 

 called the " Operculum ; " in some cases it is horny, as 

 in the Perriwinkle, and in others, resembles shell ; the 

 shells of these mollusca are coiled into a spiral, this is 

 caused by the shell always growing by additions to the 

 edges of the mouth, and in nearly every case this spiral 

 turns in the same direction that a screw does, but in a 

 very few it turns in the opposite direction, as in the 

 " Fusus contrarius." 



6. The Cephalopoda include the " Cuttle-Fish," and Nautilus 

 (fig. 33) . They are furnished with eight or ten tentacula 

 or arms, which spring from the head, and which are 

 covered with suckers ; the mouth is in the centre, and 

 these tentacula are used to lay hold of their prey and 

 convey it to the mouth ; they have two perfect eyes, 

 and they breathe by gills. The Nautilus has a univalve 

 shell, which is of a very graceful and elegant form ; its 

 interior is divided into chambers, with a syphon run- 

 ning through them, by which the air is exhausted or 

 compressed so as to cause them to sink or swim ; the 

 animal occupies only the outer chamber ; the extinct 

 Ammonite belonged to this class. It is from the Cuttle- 

 Pish (SepiaB) that the beautiful dark brown pigment, 

 known as " sepia," is obtained, and also the material 

 of which Indian-ink is made. 



