80 



BOYS AND GIRLS IN BIOLOGY. 



and some of them are prettily colored, and each one has 

 wavy knobs along its sides (Fig. 79). The bag, or body, 

 of the hydra is made of two coats ; the outer coat is 

 the ectoderm, or outer skin, the other is the endoderm, 

 or inner skin. The cells of the outer skin, in the green 



Fig. 79. 



Gkeen Hydra. 



hydra, contain color-grains, or chlorophyl, which gives 

 the green color. It is curious to see that the hydra 

 makes its fingers (Fig. 80) as the amoeba makes its feet, 

 by pushing out its two coats, the ectoderm, or outer 

 skin, then the endoderm, or inner skin ; but the hy- 



