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



quadrant. The largest velar canal lies nearest the interradial pedal and shows 6 to 8 pairs 

 of side branches, partly simple, partly cleft. On the other hand, the number and size 

 of the irregular side branches increases at intervals towards the frenulum (fig. 8). The 

 velar canals lie freely in the gelatinous fulcra! lamella of the velarium and are not 

 connected by a cathammal plate ; they are therefore secondary formations, which have 

 subsequently grown with the solid supporting plate of the velarium from the distal 

 margin of the lobe pouches. 



The four perradial rhopalar canals (or ocular vessels) arise by a funnel-shaped basis 

 from the middle line of the radial pouches above the velar frenula, and pass, narrowed, 

 immediately into the peduncle of the sense club, in whose free head part they end in 

 an ampulla-shaped expansion. The four tentacle canals (or the pedal canals leading 

 into the tentacles) arise at the four interradial angles of the umbrella by a double 

 root, as each tentacle receives a root canal from the distal corner of each quadrangular 

 radial pouch. Each pouch therefore gives out two root canals for two adjacent 

 tentacles. The junction of the two root canals takes place immediately below the 

 distal end of the septum. The tentacle canal proceeding from it traverses the entire 

 length of tentacle, and is comparatively very narrow, owing to the thickness of the 

 tentacle wall. A kind of marginal circular canal is formed by the communication of 

 the radial pouches, which is produced at their distal margin by the root canals. 



The genitalia (PI. XXVI. figs. 2, 6, 10, s) form eight broad, thin, semi-oval leaves 

 which are fastened in pairs along the four interradial septal selvages, and project freely 

 from these into the four radial pouches ; they occupy the greater part of their hollow 

 space so that the two reproductive leaves of each pouch touch each other or even overlap 

 with their free margins in its middle (fig. 2, s). Claus sees in this formation "a 

 very peculiar arrangement" (1879, Zoologie, p. 289). The difference presented 

 between the reproductive glands of the Cubomedusse, and those of the other Acraspeda, 

 is, in fact, only insignificant ; and the former may easily be referred back to the latter. 

 Most Lucernaridse show the same conditions in the broader anatomical sense, as in these 

 two genitalia come upon each of the four broad radial pouches. These, however, do not 

 belong to the said pouches, but rather to the interradial septum, which separates each two 

 pouches. The two genitalia, which belong to two adjacent pouches and are separated 

 by a septum, form one pair, and in Halicyathus, as in Tesserantha (PL XV.), are con- 

 nected into a horse-shoe by a convex arch at the proximal end of the septum. In the 

 remaining Lucemaridse (Pis. XVI., XVII.) this U-shaped connective arch has undergone 

 retrograde formation, so that eight separate adradial reproductive leaves lie beside each 

 other, and this holds good for the Peromedusae and Cubomedusae. In all cases, likewise, 

 the reproductive elements are formed from the subumbral endoderm of the radial 

 pouches (fig. 10, rw). Then the reproductive leaves are fastened to the septum in 

 such a way that they touch the umbral wall immediately ; but as they are completely 



