Beginners' zoology . ays ; theyusually have several pointed notcheswhich serve as teeth. Why should thegrasping jaws be beneath the chewing Fig. 123. — Mouth jaws . Why is it better for the lower Parts OF Beetle. i- , , c ^1 .1 i- 1 lip to have fingers than the upper hp .- Why are the fingers (or palpi) jointed ? (Watch a grasshopper or beetle eating.) Why does an insect need grasping jaws ?The chest, or thorax, consists of three rings (Fig. 124) called the front thorax (prothorax), middle thorax (mesothorax) and hind thorax (metathorax), or first, second, and third first ringbears t
Beginners' zoology . ays ; theyusually have several pointed notcheswhich serve as teeth. Why should thegrasping jaws be beneath the chewing Fig. 123. — Mouth jaws . Why is it better for the lower Parts OF Beetle. i- , , c ^1 .1 i- 1 lip to have fingers than the upper hp .- Why are the fingers (or palpi) jointed ? (Watch a grasshopper or beetle eating.) Why does an insect need grasping jaws ?The chest, or thorax, consists of three rings (Fig. 124) called the front thorax (prothorax), middle thorax (mesothorax) and hind thorax (metathorax), or first, second, and third first ringbears the first pair of legs, the second ring bears thesecond pair of legs and the upper or frontwings, and the third ring bears the thirdpair of legs and the under or hind wings. The six feet of insects are characteristic ofthem, since no other adult animals have thatnumber, the spider having eight, the cray-fish and crabs having ten, the centipedes still more, while birds and beasts have less than six. Hence the insects. Fig. 124. — External PartsOF a Beetle. I ? n 1 / Fig. 125. —Leg OF Ins INSECTS 75 are sometimes called the Six-Footed class {Hexapodd).The insects are the only animals that have the body inthree divisions. Man, beasts, and birds have only twodivisions (head and trunk). Worms are not divided. Define the class insecta by the two facts characteristic ofthem { possessed by them alone), viz. : Insects are ani-mals with and . Why would it be ambig-uous to include hard outer skeleton in this definition ? Toinclude bilateral symmetry. Segmented body.^ Thedefinition of a class must include all the individuals of the class,and exclude all the animals that do not belong to the class. The leg of an insect (Fig. 125) has five joints (two shortjoints, two long, and the foot). Named in order from above, theyare (i) the hip (coxa), (2) thigh ring (trochanter), (3) thigh(femur), (4) the shin (tibia), (5) the foot, whichhas five parts. Which of the five joints of awas
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
