IV 



PHYLUM CCELENTERATA 



99 



In the description of the fixed Obelia-colony no mention 

 was made of cells set apart for reproduction, like the ova and 

 sperms of a sponge. As a matter of fact, such sexual cells 

 are only found, in their fully developed condition at least, in 

 the medusae. Hanging at equal distances from the sub- 

 umbrella, in immediate relation with the radial canal, are 



FIG. 43. Stages in the development of two Zoophytes (A H, Laonieclea, I M, 

 Eudendrium) allied to Obelia ; A F, stages in segmentation ; G, the planula 

 enclosed in the maternal tissues ; H, the free-swimming pla'nula ; I M, fixation 

 of the planula and development of the hydrula. (From Parker's Biology, after 

 Allman.) 



four ovoid bodies (Fig. 42, gon.\ each containing a mass of 

 cells which are developed into ova or sperms. As each 

 medusa bears organs of one sex only (testes or ovaries as 

 the case may be), the individual medusae are dioecious. 

 When the gonads are ripe, the sperms of the male 



