4 6 
THE LIVING WORLD. 
COMMON SEA MOUSE. 
EARVA OF CKAB. 
or crawl with the greatest facility. Its 
snout has jaws and fringe-like tentacles, 
so that altogether it has a resemblance 
to the body of a mouse. 
The Silurian Trilobite is a fossil 
which derives its name partly from the 
geological formation in which it is fpund, and partly from its three lobes, or 
segments. The head is rounded in front, and often furnished at the back 
with long spines; the eyes, when 
present, are situated on opposite 
sides of the head, and are single, 
grouped or compound. In the 
earliest stage the body is an oval 
disc, and while there is no meta¬ 
morphosis, segmentation takes 
place as the animal develops. 
Some four hundred species have been distinguished by the faithful students 
who have devoted themselves to the study of this animal, whose advent pre¬ 
ceded our own. 
The Skeleton Screw ( Cap- 
rella linearis ), a curious creature, 
has a skeleton-like leanness, but 
likewise a voracity similar to that 
of the greyhound. The first pair 
of legs terminate in a thin, razor¬ 
like joint, notched along the edges, 
and shutting into a groove in the 
enormously large j oint above ; the 
groove has furthermore a double MANTIS SHRIMP ' 
kedgerow of spines. It supports itself on marine plants by its several pairs of 
lion to a life on land. It frequents damp places and is to be looked for under 
moss, dead leaves, and stones. It protects itself like the hedge-hog by rolling 
itself into a ball. 
The Sea Mouse (.Nereis pelagica ) is a nereid , or centipede, and has but 
little resemblance to fish. Its back is covered with a substance like flax, having 
fastened spines and iridescent bristles, 
making this animal a rival of the most 
beautiful humming-bird. It has many 
bristle-like feet, which enable it to swim 
