106 METAMORPHOSES OF MAN 



have no shell, even in the adult condition ; their head 

 is provided with four long stout horns or tentacles,, at 

 whose base a single pair of eyes may be seen ; and 

 their back is covered with little projections, which for 

 a long while had been considered simple branchiae. 

 They crawl along the bottom of the sea, by means of 

 a thick fleshy disk, which is called a foot. These 

 pretty little creatures are most brilliantly coloured, 

 and look as if they were composed of enamel and 

 crystal. So much for their external characters. In 

 the interior we find, besides other organs, a stomach, 

 which terminates in an exceedingly short intestine, 

 and gives off from its opposite side a series of more or 

 less numerous canals, which ramify, and send pro- 

 longations almost to the extremities of the dorsal 

 appendages. The liver, which is usually so extensive 

 in mollusks, is here represented by delicate glandular 

 layers which surround the terminal cceca of the gastro- 

 vascular apparatus. Let us see what these exceptional 

 mollusks are like in their earliest stages. On emerging 

 from the egg y each larva is provided with a shell, and 

 its foot, rudimentary as yet, has a sort of horny plate 

 attached to it, which it raises or lowers like a draw- 

 bridge when it wishes to close or open its shell. 

 Being unable to creep along, it is furnished with a 

 locomotive organ, in the form of a large double collar 

 placed above the mouth. The edges of this structure 

 are clothed with long vibratile cilia, which make it a 

 very powerful swimming organ, that the animal folds 

 or unfolds at will, when retreating into its shell. The 

 animal, surrounded by the latter, and fixed to it by a 

 set of strong muscles, possesses a digestive apparatus 

 and liver like those of other mollusks. After a certain 



