138 



COELENTERATA. 



that many organs of the colony which on the old colonial theory 

 are modified polyps are on this view nothing more than parts of 



medusiform indi- 

 viduals which 

 have shifted their 

 attachment, and 

 are therefore really" 

 organs. For in- 

 stance, the struc- 

 tures called pal- 

 pons (hydrocysts, 

 dactylozooids) are 

 to be looked upon 

 as mouthless ma- 

 nubria of medu- 

 soids, the um- 

 brellas of which 

 have become modi- 

 fied as bracts, or 

 are entirely degen- 

 erate. The siplwns 

 (trumpet - shaped 

 polyps, nutritive 

 polyps) are the 

 manubria of medu- 

 soids, of which the 

 umbrella is a bract, 

 or a nectocalyx or 

 degenerate. The 

 tentacle, on the 

 other hand, is to 

 be looked upon 

 only sur- 

 marginal 



tentacle of the 

 medusoid of the 

 siphon, which has 

 shifted so as to be 

 attached to the base of its manubrium. This theory then agrees 

 with the second theory in asserting the colonial nature of the 

 Siph.onoph.ora, but admits that there has been that vegetative 



as 



the 



Fio. 116. Diagram of a colony of Siphonantliae. St coenosome 

 or stem ; Ek ectoderm ; En endoderm ; Pn pneumatophore ; Sk 

 budding nectocalyx; ,S' nectocalyx; Tpalpon (hydrocyst, dacty- 

 lozooid); ,S/ tentacle and palpacle ; P siphon (polyp); mouth 

 of siphon ; Nk battery of nematocysts ; D hydrophyllium ; G 

 gonophore. 



viving 



