BIOLOGY FOR YOUNG BEGINNERS. 



353 



coats. The outer coat is the ectoderm or " outer skin," the other is 

 the endoderm or " inner skin " (Fig. 36). The cells in the outer skin 

 of the green hydra contain those green grains or chlorophyll which 

 give the green color. It is curious to see that the hydra makes its 

 fingers, or tentacles, somewhat as the amoeba makes its feet, or pseu- 

 dopodia3 (Fig. 36). It pushes out its two coats in the same way, but it 

 never allows its fingers to swallow it as the amoeba is swallowed by 



T^? " 



Endoderm. 

 Ectoderm. 



Fig. 36. Hydra pushing out its Fingers. 



its feet. When it is disturbed or frightened, it seems to swallow its 

 fingers, or rather puts them all into its mouth, like a sulky child. It 

 is a good deal higher up in the world than the amoeba, for you remem- 

 ber that had to eat with its feet. Then, too, the hydra has a more 

 aristocratic walk than the amoeba. You can see it plant its foot firmly 

 against the glass, then proudly bow its back and draw the rest of its 

 body up to the foot, in the form of a loop, like the " looping cater- 

 pillar" (Fig. 37). 



Hooks. 



Spring. 

 Cell-wall. 



Cell. 

 Coiled thread. 



Fig. 37. Looping 

 Caterpillar. 



Fig. 38. Thread-Cell. 



Fig. 39. ^ itread-Cell. 



To be sure, it goes backward, but it is a great improvement on the 

 walk of the amoeba. It is also an excellent swimmer. You may often 

 see it lift up its foot and dash into the water in search of food. It is 

 one of the funniest things in the world to see the hydra catch its prey. 

 I remember in my old geography a picture of Indians catching wild- 

 horses with lassos. The lasso is a long rope with a loop at the end, 

 vol. vi. 23 



