AVDRA. 115 
Fig. 49.—DEVELOPMENT OF THE NEMATOCYST IN 
CNIDOBLAST CELLS. 
Rudiment of Nematocyst. 
: Nucleus. 
(——— Thread. 
Cnidocil. 
and are set free by rupture of the epithelial cells. The 
ovum is produced by the growth and enlargement of a 
single germ-cell in the ovary, which appears to grow at the 
expense of the other germ-cells. It escapes by rupture of 
the epithelial cells and is a creeping amceboid cell. 
Both testes and ovaries are found in the same animal, 
hence Hydra is hermaphrodite. The testes usually appear 
and ripen prior to the ovaries, a condition known as 
protandric. 
ffydra has no definite respiratory, excretory, or sensory 
organs, and there are no nervous* nor vascular systems. 
Movement is effected by the contraction of the muscular 
* Certain stellate ectoderm cells in connection with the cnidoblasts 
have been described as nerve-cells. (See Fig. 48.) 
