243 



CCELENTEEATA. 



Pn 



S / 



FIG. 197 . Htulftemma iergtstunim. 

 S. Nectocalyx; P, polyp; JD, 



provisional appendages 

 is formed which allows 

 us to regard the develop- 

 ment of the Siphono- 

 pliora as a metamorphosis 

 (fig. 188 and 189). 



The crown of hydro- 

 phyllia, which is com- 

 pleted by the addition of 

 fresh hydrophyllia. after 

 the appearance of a 

 tentacle with provisional 

 groups of nematocysts, 

 persists only in Athory- 

 bia, where a swimming 

 column with nectocalyces 

 is never formed. 



In Agalmopsis and 

 Physophora the primary 

 hydrophyllia of the larva 

 fall off as the stem be- 

 comes larger, and are 

 replaced by nectocalyces. 



(1) Sub-order: Physo~ 

 plwridce. Stem short, 

 extended in the form 

 of a sac (fig. 190), or 

 elongated spirally (fig. 

 191), with a pneumato- 

 phore, usually nectocaly- 

 ces, which are arranged 

 in two or more rows on a 

 swimming column below 

 the pneumatophore. 

 Hydrophyllia and dacty- 

 lozooids are usually 

 present, and alternate 

 with the polyps and 

 gonophores in regular 

 order. The body of the 

 larva usually develops 



Pn, pneumatophore ; 



bydrophy Ilium ; Nk, groups of nematocysts. 



