LOO 



NATURAL HISTORY. 



banded Achatinella, while the Samoan Islands are, or were, almost equally 

 r i c h i n species of Partula. In both groups of islands these forms are being 

 rapidly exterminated. In the Samoan Islands a tornado a few years ago 



royed the plants on which the molluscs feci, while in the Hawaian 

 [slands the same result is brought about by the sheep eating the low 

 shrub on which the Achatinellce subsisted. 



Mention should here be made of the curious tropical slugs, which have 

 no common name, but which figure in the pages of scientific works 

 under the name Onchidium. They live on the shores of the ocean, above 

 low-watermark, where they creep about and feed upon vegetable matter 

 jusl Like any other slug. Most remarkable is the fact that in some of the 

 species living in the eastern seas, the whole back is covered with eyes, and 

 these organs in their structure more closely resemble those of the verte- 

 brate than those of the nearly related snails. 



Fig. 94. — Pond-snails (Lymnsea). 



Among the pulmonates are numbers of fresh-water forms occurring in 

 every pond and slow-running brook. In external appearance they have 

 little thai is attractive. Their shells are horn color or dirty brown, and in 

 life the} are usually so covered with mud and dirt that even the little natural 

 beauty they possess is hidden. Of these fresh-water forms, four types occur 

 with us. One is that figured (Lymncea). Succinea is much like it, only 

 smaller ; Physa is like Succinea, except that the shell is coiled in the oppo- 

 site direction; while in Planorbis the shell is a flat spiral, like a watch- 

 spring <>r a roll of tape. x\ll these forms are air-breathers, and are not to 



confounded with other fresh-water forms to be mentioned further on. 

 All at intervals come to the surface to obtain a supply of oxygen, climH 

 ing up the stem of some plant to the air, and there opening their lung, 

 expelling the air contained in it, and taking a new supply. 



