fore, in the case of crayfishes nothing like the parental care of higher animals.

FIG. 112.-Female lobster with eggs beneath abdomen. (Herrick's "Amer ican Lobster "-United States Fish Commission.)

117. Relatives of the crayfish.

fish is the lobster (Fig. 112), which is a salt water animal found along the north Atlantic coast. Like the crayfish, its body consists of

a cephalothorax and a clearly segmented abdomen. The lobster also has two pairs of antennæ, a pair of stalked eyes, a number of pairs of mouth parts, a pair of big claws, four pairs of walking legs, to the bases of which gills are attached, and a pair of swimmerets

on each of the segments of the abdomen except the last. In general, lobsters are very much larger than crayfishes, one of the largest known specimens weighing over twenty-three pounds.

Less like the crayfish in appearance are the crabs, yet a careful examination shows that these animals have practically all of the characteristics mentioned in the preceding paragraph. The cephalothorax of crabs, however, is usually wider than it is long (Fig. 113), and the abdomen is much reduced and is commonly folded in a groove beneath the cephalothorax. Few of the crabs are able to swim; usually they crawl sideways by the help of their four pairs of walking legs.

"A curious modification of habit is (Fig. 114), which in early life backs into an empty snail shell which aids in protecting it from its enemies. The abdomen, thus covered, becomes soft and flabby. As growth proceeds the necessity arises for a larger shell, and the crab goes 'house-hunting' among the empty shells along the shore, or it may forcibly extract the snail or other hermit from the home which strikes its fancy."- JORDAN and HEATH, "Animal Forms."

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Among the relatives of the crayfish that live in damp places on land are the pill bug and the sow bug (Fig. 115) which are often found beneath water-soaked wood. All the animals we have described in this chapter belong to the class Crustacea, so-called from the hard outer shell which invests them.

FIG. 115. The sow bug.

118. Economic importance of the Crustacea. Crayfishes in Europe, particularly in France, are highly esteemed as food, and special efforts are made to increase their number. In this country, however, they have, as yet, been used but little as food. Their principal use is for bait in catching certain kinds of fish.

The lobster is to us what the crayfish is to Europeans. While they are not abundant enough to be considered a very important source of food, still the fishermen in 1901 received $1,400,000 for the lobsters

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FIG. 116. The shrimp.

caught. They are considered rather as a delicacy, since they are too expensive for general use, principally on account of their scarcity. For a number of years the United States government has been making efforts to increase the number of lobsters by artificial propagation. Some states have passed laws forbidding the catching of immature lobsters and lobsters with eggs attached.

Other crustacea that are used for food are prawns, shrimps (Fig. 116), and certain kinds of crabs. Nearly all the crustacea eat dead animal food; consequently they are useful in keeping the water free from dead material.

CHAPTER VI

PARAMECIUM AND ITS RELATIVES

119. Study of the paramecium. - Laboratory study.

Note to Teacher. - To secure paramecium material, add some chopped hay to a large jar of water several weeks before the animals are needed. The paramecia develop more rapidly and are of larger size if the water is secured from a stagnant pool. The hay infusion furnishes food for bacteria upon which the single-celled animals feed. To obtain the paramecia, transfer to a glass slide with a pipette a drop from near the surface of the water.

A. General appearance of paramecium.

1. Place a drop of water containing many paramecia or other similar forms on a glass slide (with concave depression if possible). Examine with a magnifier.

Describe the appearance of the tiny bodies that you see moving about.

2. Now examine the drop of water with the low power
of the compound microscope. Do not allow
the water to evaporate entirely, but keep adding
a little from time to time.

a. Do the paramecia swim slowly or rapidly?
b. Is the more pointed end of the animal usually
foremost in swimming or the rounded end?

B. Structure of paramecium.

Secure a stained and mounted specimen of a paramecium, or add a drop of iodine solution to the water containing the living animals, and