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



right angles into the corresponding pieces of the marginal canal. The marginal canal 

 ("canalis marginalia," cm) which runs along the proximal side of the urticating ring, is not 

 however the usual marginal " circular canal " of the Medusae margin, but consists of 

 eight completely distinct pieces, separated from each other by the distal ends of the 

 peronia. Each of these independent " octants of the marginal canal " runs at the two 

 ends into a peronial canal, the two branches thus forming a horseshoe-shaped "lobe 

 canal." Each lobe canal opens with two separate mouths into the gastral cavity beside 

 the base of insertion of each two tentacles. The two peronial canals of each double 

 canal and their two gastral openings (at both sides of a tentacle) therefore belong to two 

 different "lobe canals." The eight lobe canals form collectively the eight-lobed 

 " festoon canal," and this is phylogentically only a peculiar modification of the 

 primarily simple "circular" canal, caused by the dorsal change of position of the 

 tentacles and the formation of peronia connected with it. 



The sixteen subradial reproductive pouches of JEginura show essentially the same 

 formation already described by Mertens in jEginopsis laurentii (1838, loc. cit. PI. VI.). 

 They are quadrangular, almost rectangular, and distributed in such a way that a large 

 and a small pouch is placed on each of the eight collar lobes (PI. XIII. fig. 1, 2). The 

 pouches, consequently, lie in internemal pairs, a pair between each two tentacles and 

 peronia. It appears, however, on closer inspection that, as in ^ginopsis laurentii, all 

 the sixteen pouches actually belong to four primary groups. Two smaller pouches are 

 placed on both sides of the four larger perradial tentacles, and two larger pouches on both 

 sides of the four smaller interradial tentacles. If the whole umbrella be divided into 

 four quadrants, whose middle lines form the four perradial peronia and the border lines 

 the four interradial peronia, a group of pouches consisting of two small medial pouches and 

 two large lateral pouches falls in each of the quadrants. The same condition is shown, 

 if we suppose each of the eight lobe pouches of Cunarcha already described (PI. IX. 

 figs. 2-4, bl) divided by a centripetal incision of their distal margin into two pouches 

 of unequal size, and the four proximal (perradial gastral pouches), formed by the bifur- 

 cation of the eight lobe pouches, to have undergone retrograde formation. It is then clear 

 that each group of four associated reproductive pouches belonging together in JEginura, 

 is simply the double bifurcated distal part of a perradial gastral pouch, whose undivided 

 proximal part has undergone retrograde formation (or become part of the central stomach). 



In fact, it is only by such morphological comparison that we can understand phylo- 

 genetically the remarkable and varied conditions of vascular formation in the iEginidas. 

 The peculiar, apparently isolated, gastrovascular system of the iEginida?, is, therefore, 

 naturally derived from that of the Cunoctonidse, from those Cunanthidfe {Cunarcha, 

 Cunoctona, Cunissa) in which each radial canal (or each "pernemal gastral pouch") is 

 cleft at the distal margin into two csecal lobe pouches. If these paired lobe pouches 

 become larger, and the undivided proximal piece of the pernemal gastral pouch under- 



