MANTLE-COVERED ANIMALS. 123 
other animals, as for example the little testacella (B, 
Fig. 46), a queer little fellow which follows the worms 
down into their holes, and drags them down his 
throat by his rasp of barbed teeth, so that often 
several worms may be found torn and mangled 
within his body. His breathing chamber has found 
its way nearly to the end of his tail, so that he can 
breathe when the front of his body is buried, while 
the little shell (s) which covers it looks very comi- 
cal, but is useful, nevertheless, in protecting it from 
attack behind. 
All these many forms of water-snails, and land- 
snails, and slugs, have taken possession of the land 
and its waters, and now if we go back to the sea we 
find that the world has still room for other kinds, 
only they must fit into gaps that are not occupied. 
For wonderfully beautiful mantle-covered creatures 
may be found there lurking under stones and in dark 
corners, if a careful search is made at low tide. These 
are commonly called " sea-slugs," and by scientific 
men the " naked-gilled " mollusca, because they have 
no shell or covering over their feather- like gilli 
Of <"> Fig. 47), but carry them erect on their backs 
like tufts of moss or delicate seaweed. Yet in theii 
babyhood these naked animals lived in a tiny curled 
shell, and swam about by lashes like the young of all 
the stomach-footed animals, and we can still recognise 
their nationality, by their feathery gills and their 
coiled rasping tongue. Like the land-slugs they can 
creep through many a narrow opening not possible 
for shelled animals, and though their eyes are not 
powerful they have very sharp ears, a quick sense of 
