SORTING OF ANIMALS 5 
in certain parts of the country. Ah example of thread worms is the 
dreaded trichinae, which infest pork. Leeches also. belong to the 
worm group. In ascending the scale worms are the first great group 
of animal life in which true land animals are found. 
7. Arthropoda.—The crustacea, or jointed animals of the 
water, breathe by gills. The insects, or jointed animals of 
the land, breathe through tubes in their sides. 
Crabs and lobsters belong to the first group, 
and insects and spiders to the second. True 
spiders have eight legs, whereas the true in- 
sects have six. Spiders dispose of their prey 
by sucking and never swallow solid food. All 
spiders have poison glands, certain varieties 
being very venomous. Scorpions and centi- 
pedes belong to the spider division. The num- 
ber of insects is enormous, some authorities 
placing it at a quarter of a million. Bees, ants, 
beetles, fleas, locusts, weevils, and the various kinds 
known as insect pests, all belong to this group. 
LIVER FLUKB 
“We owe the bright colors and the sweet honey of flowers to the 
selection exercised by insects; they carry the pollen of flowers from 
one plant to its neighboring kindred, thus securing cross- 
fertilization for the advantage of the plant, and thereby 
perpetuating any quality, such as color or sweetness, which 
has originally attracted the insect to the flower. While a 
few plants only are fertilized by means of the wind, a vast 
majority depend entirely upon insects for the cross-fertiliza- 
tion which is so necessary for the production of healthy 
seeds. If the earthworm has been the plowman, the insect 
has been the more intelligent gardener, who has filled the 
world with bright flowers. The insect owes its food to the 
plant world; the plant world owes health and beauty to the 
constant ministration of the insect.” 
8. Moilusca.—An insect is covered by a hard- 
ened skin. In the mollusk, or shellfish, a cover- pyar. 
ing is secreted which lies outside the skin. Just as WR 
our skins pass perspiration out to the surface, so the skin 
of these animals passes to the outside certain substances 
that the body has taken in from the sea water. As these 
