HYDRA. 



115 



Fig. 49. — Development of the Nematocyst in 

 Cnidoblast Cells. 



Rudiment of Nematocyst. 

 Nucleus. 



Thread. 



and are set free by rupture of the epithelial cells. 7^he 

 ovurii 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 amoeboid 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 

 prota7idric. 



Hydra 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.) 



