16 THE VOYAGE OF H.M.S. CHALLENGER. 



POLYSIPHONLE on POLYGASTRIC SIPHONOPHOILE. 



In the great majority of Siphonophorse the adult form possesses several suctorial tubes 

 or polypites as organs for the reception and digestion of food. These arise in the Dis- 

 conanthse by budding from the primary subumbrella, in the Siphonanthse on the other 

 hand by budding from the ventral middle line of the primary siphon, which is modified 

 into the stem. In the former these " metasiphons " surround the primary archisiphon as 

 a corona ; while in the latter they are disposed upon the protosiphon either on the one 

 side only or on all sides, in a spiral line. In the simplest and most primitive case, such as 

 occurs in the polygastric Calyconectae and in many Physonectse, the metasiphons develop 

 in regular metameric succession on the segmented stem, separated by wide internodes. 

 Each individual siphon is (in the Eudoxix and the corresponding simplest Prodoxim of 

 the Physonectse) associated with a covering bract ; both together form a medusome, the 

 umbrella being represented by the bract, the manubrium by the siphon. In most of 

 the Physonectae numerous covering bracts soon develop, which are to be considered as 

 mere multiplications of the primary bract, and therefore as entirely subordinate organs. 

 But when from the base of such a medusome gonophores bud forth — appendages that is 

 to say of the morphological value of a meclusoid person — then such a " group of persons " 

 acquires the value of a cormidium. In many Polysiphonise the metameric arrangement 

 Of the cormidia subsequently breaks up, and then the connection between the scattered 

 siphons and the separated sexual medusomes is often no longer demonstrable. 



PALPONS or TASTERS. 



{Feelers, Tasters, Arms, Fluid Receptacles, Hydrocysts, Dactylozooids.) 



In the great majority of the Siphonophoraa, the siphosome bears, scattered between the 

 siphons, or connected in groups with the latter, the tasters or feelers. These are always 

 simple, thin-walled, very contractile sacs, in which the proximal portion communicates 

 with the cavity of the stem, while the distal end is closed. Morphologically the tasters 

 are to be regarded as mouthless manubria, or as the stomachic sacs of medusomes in 

 which the umbrellas have become modified into covering bracts or are entirely degenerate. 

 The palpons are distinguished from the cystons by the absence of a distal opening, from 

 the siphons not in this alone, but also in the absence of the glandular villi and hepatic 

 stripes in the stomach region. Their function appears to be mainly, if not exclusively, 

 sensory. Their sensitive point probably acts generally as a taste organ, and sometimes 

 also as an eye ; in a (new) Athorybia I observed a lens in this ocellus (a sickle-shaped 

 pigment spot on the upper surface of the sensory apex). In some Agalmidaa the distal 



