THE SEA-ANEMONE AND SOME ALLIES 265 



-3 



Reproduction may take place by the sexual method, or by 

 budding. Eggs (Fig. 131, 9) are developed in the ectoderm 

 near the aboral end. In the same 

 individual spermatozoa (Fig. 

 131, 8) are formed in the ectoderm 

 nearer the oral end, and these on 

 escaping fertilize the eggs, which 

 remain in the ectoderm for some 

 time as embryos. Then the em- 

 bryos separate from the parent, 

 and after swimming about for a 

 variable period develop into 

 organisms like the parent. Non- 

 sexual reproduction is the more 

 frequent method, however. Buds 

 involving both ectoderm and 

 endoderm form on the side of the 

 body (Fig. 131, 3, 4) ; four tenta- 

 cles appear, the mouth forms, and 

 the base of the bud constricts, 

 setting the young Hydra free to 

 begin its own career. 



Hydroids and Medusae. There 

 is a large group of animals closely 

 allied to Hydra, that live in the 

 sea. A portion of one of them, 

 Bougainvitfliafrutieo'sa, is shown 

 in Fig. 132. It looks very much 

 like a plant, owing to its habit of 

 branching. The colony may con- 

 tain many polyps, each of which 



is connected indirectly with every other by means of the 

 continuous body-wall. At the base of the colony, root-like 

 branches from a stem-like structure cling to floating timbers 



FIG. 132. Hydroid. Much en- 

 larged. (After Allman) 



1, tentacles; 2, 3, 4, stages in the 

 formation of medusa 



