IIYDROZOA Sll'HOXOPIIOBA. 



243 



Order 2. SIPHONOPHORA.* 



Free-swimming polymorphous hydroid-stocks with contractile stem, 

 with polypoid 

 nutritive indi- 

 viduals and 

 medusoid buds, 

 usually also 

 with nectocaly- 

 ces, hyrophytticti 

 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 o f 

 their polypoid 

 and medusoid 

 appendages. 

 The functions 

 of he latter 

 seem so inti- 

 mately con- 

 nected and are 

 so essential for 

 the preserva- 



/ 



FIG. 185. Diagram of a colony of Pliysophorida. /SV, Stem; ETc, 

 ectoderm; En, cntoderm ; I'n, Pneumatophor; Sk, nectocalyx 

 beinR budded off; 5, nectocalyx; D, hydrophyllimm ; 6f, pono- 

 phore; T, daetylozooid; Sf, tentacle ; P, polyp; O, mouth of the 

 latter ; Nk, battery of nernatocysts. 



i 



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



* Besides Kolliker, C. Vogt, Huxley and others, compare C. G-egenbaur, 

 " Beobachtuogen liber Siphonophoren," Zcitschrift fur wixtt. Znol., 1853. C. 



