REPORT ON THE SIPHONOPHOR^. 293 



a regular pavement composed of innumerable small paliform cnidocysts (tk u ). The strong 

 cnidofilament protruded from the large bean-shaped cnidocysts is a rather thick and 

 spirally convoluted thread (PL VII. fig. 43, A, b). The slender terminal filament of the 

 tentilla (fig. 23, tf) is a simple cylindrical blind tube, scarcely half as broad as the 

 battery, and armed with roundish cnidocysts of medium size. 



Gastro-canal System. — The system of nutritive vessels of the Auronectse is more 

 complicated than that of the other Siphonophorae (with the exception of the Disconectae). 

 It is composed of the following parts : — (1) The central hypocystic cavity of the trunk 

 (PI. IV. fig. 15, aa; PI. VII. fig. 40, ah) ; a large circular horizontal cavity of 

 discoidal form, the apical wall of which is formed by the lower part of the pneumato- 

 phore, the basal w r all by the uppermost part of the siphosome. (2) The pericystic cavity 

 ofthepneumatosaccus (PI. V. fig. 24, ps), enclosed between the thicker outer and the 

 thinner inner wall of the pneumatophore ; it gives off small irregular lateral branches 

 which pierce the thick wall of the pneumatocodon (fig. 30). (3) The cavity of the 

 aurophore (PI. V. figs. 24-26, Ir), divided by numerous irregular, partty radial, partly 

 branched septa into a spongy system of lacunar vessels and radial chambers ; the 

 basal part of the aurophore-cavity communicates on its upper side with the cavity of 

 the pneumatophore (fig. 24, ps), on its lower side with the central main cavity. (4) 

 TJie reticulum of truncal canals (PI. IV. fig. 15, ac; PI. VII. fig. 40, ac), composed of 

 a dense network of numerous irregularly branched and anastomosiug vessels, which 

 pierce the thick cartilaginous bulbs of the trunk in every direction ; the centre of this 

 truncal reticulum is in Stephalia the axial central canal (fig. 40, ca) descending 

 vertically from the centre of the main cavity towards the basal central siphon and 

 opening through its mouth. (5) The ventral budding canal (PI. IV. fig. 16, ic), 

 running from the ventral median line of the central hypocystic cavity to the 

 ventral series of buds (i), and giving off a lateral branch to each bud. (6) The 

 nectocalycine ducts, or the peduncular canals of the nectophores (PL V. fig. 31, ns), 

 arising from the stem-cavity, running horizontally along the basal edge of the peduncle, 

 and giving off a unilateral series of lateral branches which ascend vertically (fig. 31, nl). 

 (7) The four radial canals of each nectophore (PL IV. fig. 17, nr ; PL VII. fig. 39); 

 they arise crossed from the distal end of the peduncular canal, run along the sub- 

 umbrella towards the margin of the nectophore, and are there united by a circular canal 

 (fig. 39, cc). (8) The central caned of each cormidium, and the network composed of its 

 anastomosing branches, often united by subregular elegant arches with the network of the 

 neighbouring cormidia. (9) The simple siphon cavity (PL I. fig. 4, c) composed of four 

 segments (pedicle, basigaster, stomach, and proboscis); it arises from \h.e superficial canal- 

 network of the cormidium and wives off from the basigaster a lateral branch for the tentacle 

 (tentacular canal, PL IV. fig. 21, c). (10) The simple gonostyle canal (PI. I. figs. 2, 3, c ; 

 PL II. figs. 7, 8 ; PL VII. fig. 49), arising from the superficial canal network of the 



