278 



BIOLOGY 



plication by budding, is the asexual stage, and is comparable 

 to the asexual stage of the fern above described (the fern 

 proper). It differs from the fern, however, in the fact' that ?t 

 does not produce new individuals by spores, but by budding. 

 After a colony reaches a certain stage in its growth, some 

 buds arise which differ in shape from the others. These (Fig. 

 129 gb) are rounded, and eventually break away from the 



FIG. 129. A COLONY OF HYDROIDS (PODOCORYNE), SHOWING AN ALTER- 

 NATION OF GENERATIONS 



The feeding animals have tentacles; gb, the generative buds, which eventually break away 

 and become medusae; m, medusa; mo, mouth of the jellyfish; ov, ovaries. 



Colony and assume an independent existence. These free buds 

 now become bell-shaped individuals of clear, transparent 

 jelly, and are known as jellyfishes or medusae, m. The jelly- 

 fishes have muscles which enable them to swim and travel 

 for long distances in the ocean. As they have a mouth 

 and digestive cavity they can procure their own food, and grow, 

 frequently attaining considerable size after separating from the 

 original colonies; some species, indeed, assume a size very 

 much larger than the animal that produced them. After hav- 

 ing lived this free life for a time, each becomes sexually mature, 

 developing sexual glands, either ovaries or spermaries; Fig. 130 g. 

 The sex bodies become mature, and are extruded into the water, 



