. Essentials of biology presented in problems. Biology. THE VERTEBRATE ANIMAIS 295 <^ Snakes. — Probably the most disliked and feared of all animals are the snakes. This feeling, however, is rarely deserved, for, on the whole, our common snakes are beneficial to man. The black snake and the milk snake feed largely on injurious rodents (rats, mice, etc.), the pretty green snake eats injurious insects, and the little DeKays snake feeds partially on slugs. If it were not that the rattlesnake and the copperhead are venomous, they also could be said to be useful, for they live on English sparrow
. Essentials of biology presented in problems. Biology. THE VERTEBRATE ANIMAIS 295 <^ Snakes. — Probably the most disliked and feared of all animals are the snakes. This feeling, however, is rarely deserved, for, on the whole, our common snakes are beneficial to man. The black snake and the milk snake feed largely on injurious rodents (rats, mice, etc.), the pretty green snake eats injurious insects, and the little DeKays snake feeds partially on slugs. If it were not that the rattlesnake and the copperhead are venomous, they also could be said to be useful, for they live on English sparrows, rats, mice, moles, and rabbits. Snakes are almost the only legless vertebrates. Although the Umbs are absent, stiU the pelvic and pectoral girdles are developed. The very long backbone is made up of a large number of ^ertebria?, as many as four hundred being found in the boa con- strictor. Ribs are attached to all vertebrse in the region of the body cavity. Locomotion.—Locomotion is performed by puUing and pushing the body along the ground, a leverage being ob- tained by means of the broad, flat scales, or scutes, with which the ventral side of the body is covered. Snakes may move without twisting the body. This is accomplished by a regular drawing forward of the scutes and then pushing them backward rather violently. Feeding Habits. — The bones of the jaw are \'ery loosely joined to- gether. Thus the mouth of the snake is capable of wide distention. It holds its prey by means of incurved teeth, two of which (in the poisonous snakes) are hoUow or grooved, and serve as a duet for the passage of poison. The poison glands are at the base of the curved fangs in the upper jaw. The tongue is very long and cleft at the end. It is an organ of touch and taste, and is not, as many people believe, used as a sting. The food is swaUowed whole, and pushed down by ryhthmic contractions of the muscles surrounding the gullet. They usually refuse other than living prey. Adaptations. —
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
