66 



SYSTEMATIC ZOOLOGY 



a single row of tentacles, which are often very long, and they 

 live singly, not forming colonies. As they reproduce chiefly by 

 budding, temporary colonies are sometimes found, but the young 

 individuals eventually separate from the parent and attach them- 

 selves to some foreign object (Fig. 49). Sexual reproduction 



FIG. 49. 1. Hydra viridis, the green hydra as it appears in autumn with germ- 

 glands. Below the ring ot tentacles appear three testes containing sperma- 

 tozoa; nearer the attached end is the egg-zone, showing two ova indifferent 

 stages of development. 2. Hydra vulgaris, the brown hydra as it appears 

 in spring — buds developing in place of sexual organs, which form in the 

 autumn. (Photographed from a Leuckart-Nitsche wall-chart, by the author; 

 permission of Dr. C. Chun.) 



also occurs, and the ova and spermatozoa are formed from ecto- 

 dermal cells, both on the same individual, which is therefore 

 hermaphroditic. This group is represented by the genus Hydra, 

 from which the order takes its name. 





