PEDIGREE OF CCELENTERA. 



159 



we have jelly fish wholly free (Pelagia), jelly fish with a 

 sedentary larval life (Aurelta), jelly fish predominantly pas- 

 sive (Lucernaria\ and related polypes (Sea anemones, &c.), 

 which only occasionally rise into free activity ; while in the 

 other series we have medusoid types always free (Trachy- 

 medusae), others which are liberated from (Campanularian 

 and Tubularian) sedentary hydroids, other (Sertularian and 

 Plumularian) zoophytes whose buds though often medusoid- 

 like are not set free, and finally. Hydra, which, though it 

 may creep on its side, or walk on its head, is predominantly 

 a sedentary animal, without any youthful free swimming 

 stage. It must be noticed that the most frequent larval 

 form is the planula, so that if we regard the gastrula as the 

 ancestral type, the life history is not here a recapitulation of 

 the race history. 



GENERAL SCHEME OF CCELENTERA. 



\6. Hydra without any specially locomotor stage. 



