THE ANIMAL KINGDOM 



395 



Chlorohydra viridissima, also known as Hydra viridis, the 

 common fresh-water hydra, colored green by algae in the 

 endodermal cells, has a polyp stage only. Gonionemus mur- 

 bachi, a marine, craspedote medusa (i.e., having a velum extend- 

 ing inward from the edge of the subumbrella), has practically 



Fig. 224. — Aurelia, a jellyfish, and stages in the life history. A, vertical 

 section of adult; B, vertical section of gastrula; C, polypiform larva with eight 

 tentacles; D, scyphistoma with sixteen tentacles, in beginning of strobilation; 

 E, strobila; F, ephyra, which develops into a jellyfish, g, gastral cavity; go, 

 gonad; m, mouth; o, oral lobe; t, tentacles. {After Leuckart-Nitsche wall chart.) 



a medusa stage only, its polyp stage being minute and of short 

 duration. Obelia dichotoma, a marine form, has a definite 

 alternation of generations, the colonial polyp producing sexual 

 buds (gonosomes) that develop into free-swimming male and 

 female medusae. The fertilized egg develops into a polyp 

 (Fig. 222). Physalia pelagica, the Portuguese man-of-war is 



