iv PHYLUM CCELENTERATA 107 



a deep blue colour, and long retractile tentacles, sometimes 

 several feet in length, and containing batteries of stinging 

 capsules powerful enough to sting the hand as severely as 

 a nettle. The male reproductive buds remain attached 

 and take the form of sporosacs, while the female apparently 

 become detached as free medusae. 



In such a Siphonophoran as Halistemma (Fig. 48), on 

 the other hand, there is a long, slender, flexible stem or 

 ccenosarc, at the upper end of which is a comparatively 

 small float. Next to this come a number of closely set, 

 transparent structures (nct.\ having the general characters 

 of unsymmetrical medusae without manubria, each being 

 a deep, bell-like body, with a velum and radiating canals. 

 During life these swimming-bells or nectocalyces contract 

 rhythmically i.e., at regular intervals thus serving to 

 propel the entire organism through the water. Below the 

 last nectocalyx the character of the structures borne by the 

 stem changes completely : they are of several kinds, and 

 are arranged in groups which follow one another at regular 

 intervals. 



Some of these are unmistakable polypes (/.), differing, 

 however, from those we have hitherto met with, in having 

 no circlet of tentacles round the mouth, but a single, long, 

 branched tentacle (/.) arising from its proximal end, and 

 bearing numerous groups or " batteries " of stinging-cap- 

 sules (ntc.\ Others are dactylozooids or feelers (dz.) 

 mouthless polypes, each with an unbranched tentacle 

 springing from its base. Near the bases of the polypes and 

 dactylozooids spring groups of sporosacs (B, s, /), some 

 male, others female ; and finally delicate, leaf-like transpar- 

 ent bodies the bracts or hydrophyllia (hph.) partly cover 

 the sporosacs. 



