HTDEOZOA SIPHONOPHOttA. 



243 



Order 2. SIPHONOPHORA.* 



Free- swimming polymorphous hydroid-stocks with contractile stem, 

 with polypoid 

 nutritive indi- 

 viduals and 

 medusoid buds, 

 usually also 

 with nectocahj- 

 ces, hyrophyllia 

 and dactylo- 

 zooids. 



Morphologi- 

 cally the Sipho- 

 nophora are 

 directly allied 

 to the hy- 

 droid-stocks; 

 but they possess 

 to a much 

 greater extent 

 than the latter 

 the characters 

 of individuals, 

 in consequence 

 of the highly 

 developed poly- 

 morphism of 

 their polypoid 

 and medusoid 

 appendag es. 

 The functions 

 of the latter 

 seem so inti- 

 mately con- FIG. 185.-Diagram of a colony of Physophonda. St, Stem; Ek, 

 nected and are ectoderm; En, entoderm; Pn, Pneumatophor; Sk, nectocalyx 



beinpf budded off ; S, nectocalyx ; 2>, hydrophyllium ; <?, gono- 

 SO essential for phore; T, daatylozooid ; Sf, tentacle ; P, polyp ; O, mouth of the 



the preserva- latter ; Nk > battery of n e ma tocysts. 



tion of the entire colony that we may regard each colony of Sipho- 



* Besides Kolliker, C. Vogt, Huxley and others, compare C. Gegenbaur, 

 " Beobachtungen liber Siphonophoren," ZeUtchrift fur wit*. ZooL, 1853. C. 



