1. _Siphons_ or nutritive appendages, from which the order takes its name; never absent and usually present in great numbers (fig. 68, e). Each is a tube dilated at or towards the base and containing a mouth at its extremity, leading into a stomach placed in the dilatation already mentioned. The siphons have been compared to the manubrium of a medusa-individual, or to polyps, and hence are sometimes termed gastrozoids. 2. _Palpons_ (fig. 68, g), present in some genera, especially in Physonectae; similar to the siphons but without a mouth, and purely tactile in function, hence sometimes termed dactylozoids. If a distal pore or aperture is present, it is excretory in function; such varieties have been termed "cystons" by Haeckel. 3. _Tentacles_ ("_Fangfäden_"), always present, and implanted one at the base of each siphon (fig. 68, f). The tentacles of siphonophores may reach a great length and have a complex structure. They may bear accessory filaments or _tentilla_ (f'), covered thickly with batteries of nematocysts, to which these organisms owe their great powers of offence and defence. 4. _Palpacles_ ("_Tastfäden_"), occurring together with palpons, one implanted at the base of each palpon (fig. 68, h). Each palpacle is a tactile filament, very extensile, without accessory filaments or nematocysts. 5. _Bracts_ ("_hydrophyllia_"), occur in _Calycophorida_ and some _Physophorida_ as scale-like appendages protecting other parts (fig. 68, l). The mesogloea is greatly developed in them and they are often of very tough consistency. By Haeckel they are considered homologous with the umbrella of a medusa. [Illustration: From G. H. Fowler, after A. Agassiz, Lankester's _Treatise on Zoology_. FIG. 70.--Diagram of the structure of _Velella_, showing the central and peripheral thirds of a half-section of the colony, the middle third being omitted. The ectoderm is indicated by close hatching, the endoderm by light hatching, the mesogloea by thick black lines, the horny skeleton of the pneumatophore and sail by dotting. BL, Blastostyle. C, Centradenia. D, Palpon. EC, Edge of colony prolonged beyond the pneumatophore. G, Cavity of the large central siphon. M, Medusoid gonophores. PN, Primary central chamber, and PN', concentric chamber of the pneumatophore, showing an opening to the exterior and a "trachea." S, Sail.]