Beginners' zoology . tive motion thanlocomotion. It seldom moves from its place, but its ten-tacles are constantly bending, straightening, contracting,and expanding. The body is also usually in motion, bend-ing from one side to another. When the tentacles ap-proach the mouth with captured prey, the mouth (invisiblewithout a hand lens) opens widely, showing five lobes orlips, and the booty is soon tucked within. A hydra canswallow an animallarger in diameter than itself. The endoderm cells \\ amceboid motion, that is, theyextend pseudopods. They also resemble amoebas in thepower of intra-ce
Beginners' zoology . tive motion thanlocomotion. It seldom moves from its place, but its ten-tacles are constantly bending, straightening, contracting,and expanding. The body is also usually in motion, bend-ing from one side to another. When the tentacles ap-proach the mouth with captured prey, the mouth (invisiblewithout a hand lens) opens widely, showing five lobes orlips, and the booty is soon tucked within. A hydra canswallow an animallarger in diameter than itself. The endoderm cells \\ amceboid motion, that is, theyextend pseudopods. They also resemble amoebas in thepower of intra-cellnlar digestion; that is, they absorb theharder particles of food and digest them afterwards, re-jecting the indigestible portions. Some of these cells haveJlagclla (see Fig. 39) which keep the fluid of the cavityin constant motion. Sometimes the hydra moves after the manner of a smallcaterpillar called a measuring worm, that is, it takeshold first by the foot, then by the tentacles, looping its 28 BEGINNERS ZOOLOGY. body at each step. Sometimes the body goes end over end in slow somersaults. The length of the extended hydra may reach one half inch. When touched, both tentacles and body contract until it looks to the unaided eye like a round speck of ielly. This shows 40.— Hydroid Colony, with ? nutritive (/°) reproductive (71/) and and a fcW Small Star-shapcd defensive (5) hydranths ^^^jjg ^^.g believed to be iierve cells, but the hydra has not a nervous system. Hydrasshow their liking for light by moving to the side ofthe vessel or aquarium whence the light comes. The Branch Polyps^sometimes called Cceleii-teratd). ~ The hydra isthe z\\\Qifresh-water rep-resentative of this greatbranch of the animalkingdom. This branchis characterized by itsmembers having onlyone opening to the polyps also includethe salt water animalscalled hydroids, jelly-fishes, and coral polyps. Hydroids. — Figure 40shows a hydroid, orgroup of hydra-likegrowths, one of whic
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
