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



cormidium and possess a distinct mouth- opening and a tentacle ; these are not 

 recognisable in a greater number of smaller and thinner spindle-shaped tubes, which arise 

 between the former ; they may be either young and undeveloped siphons, or perhaps 

 palpons which remain permanently mouthless. The difference between siphons and 

 palpons in Salacia does not seem to be sharp, as in Physalia. All the components of each 

 cormidium arise from the node of the trunk so densely crowded that it is impossible 

 to determine whether there is any close relation between the clustered gonodendra and 

 the siphons. 



Siphons (figs. 4, 5, s). — The fully developed polypites are slenderly spindle-shaped, 

 attain in the expanded state a length of 8 to 12 mm., a breadth of about 1 mm., and are 

 very similar to those of Physalia and Alophota (PI. XXVI.). The four usual segments 

 are sometimes recognisable in the strongly contracted siphon (fig. 5). The short pedicle 

 bears a subspherical basigaster with thickened exoderm (sb) ; from its base arises the 

 tentacle (t). The wide stomach (sm) is covered inside with numerous pigmented 

 hepatic villi (sv). The contractile proboscis (sr) opens at the distal end by a mouth 

 which is often expanded in the form of a roundish or circular suctorial disc ; its margin is 

 armed with a ring of cnidocysts (fig. 4, so). 



Tentacles (t). — The single long tentacle which arises from the base of each fully 

 developed siphon is very similar to those of Physalia, a simple cylindrical tube with an 

 excentric canal. The dorsal side of the tube bears a series of very numerous reniform 

 cnidonodes, whilst the ventral side is naked (compare PL XXV. figs. 4, 5, t, and 

 PI. XXVI. figs. 1-6, t). 



Gonodendra (figs. 4, g, 7). — The clustered gonodendra, which arise from each node 

 between the siphons, have a richly branched gonostyle. Each ultimate branch (PI. XXV. 

 fig. 7) exhibits essentially the same structure as in Physalia, and is composed 

 (PI. XXVI. fig. 8) of a single large gynophore (f, a medusiform umbrella with four radial 

 canals, the manubrium of which develops after the detachment), a clustered group of 

 smaller club-shaped androphores (h), and a number of gonopalpons (gq). 



Family XXIII. Epibulidj:, Haeckel, 1888. 



Definition. — Cystonectse polygastricse with a short inflated trunk of the vesicular 

 siphosome, which is spirally convoluted beyond the basal side of the large subvertical 

 pneumatophore. Cormidia ordinate in a spiral ring, protected by a corona of paljDons. 

 Pneumatosaccus without radial septa and pericystic radial pouches, but with eight or 

 more radial groups of hypocystic villi. 



The family Epibulidae represents a new interesting group of Cystonectse, which was 

 very imperfectly known up to this time. Two species only of Epibidia, both captured 



