170 



ANARTHROPODA 



breaks loose from the parent and leads an independent 

 life. 



The egg which is merely an enlarged and specialized cell 

 near the base of the parent may develop into a complete 

 polyp (Hydra) if one of the numerous male (sperm) cells 

 breaking out of the spermary unites with it. Soon after 



FIG. 197. Longitudinal section of a Hydra ; b, bud which will form a young one ; 

 6a, base by which it is attached when not creeping ; m, mouth ; ov, ovary with 

 an egg ; sp, spermary. 



the union, the egg separates from the parent and dropping 

 to the bottom may remain there over winter before growing 

 into a new animal. 



Hydroids. These are hydralike animals living in the 

 ocean, and frequently growing in colonies. Obelia is a 

 common example on our eastern coast. It is found in 

 colonies attached to boards and seaweeds near the surface 

 of the water. The animals composing the colony are called 



