CNIDARIA AS THE ONLY COELENTERATA 



67 



Fig 13. Medusoid forms as cases of parallelism. A, a phytoflagel- 

 late, Medusochloris phiale (after Pascher). B-C, two heterotrophic 

 dinoflagellates: 'Leptodiscus mednsoides (from Hertwig) and Cras- 

 pedoiella pileolus {2ihct Kofoid). D, an anthomedusa; E. a scyphome- 

 dusa; F, Pyrosoma sp. a colony (cormus) of tunicates. 



of mutations) have given similar results. Perhaps we could 

 speak of a medusoid form in Pjrosoma among Chordata, yet 

 in this case we have actually a cormus and not an individual. 

 Something similar can be observed in Chondrophora among 

 the Siphonophora. The same is actually true for the polypean 

 form too, yet with the difference that the polypean form occurs 

 much more frequently in the animal world since it is connected 

 with a semi-sessile or to a completely sessile way of Ufe. The 

 form of polyps is an oblong rotund form which is set upright on 

 a firm ground. The oral opening occurs, with the exception of 

 Protozoa and Spongiae, at its free end. The tentacle-like ex- 

 crescences grow regularly all around this oral opening in the 



