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



here as in all other Craspedotse, i.e., four narrow perradial canals communicating by a 

 coronal canal at the umbrella margin. This original formation only undergoes peculiar 

 modifications, which appear to be influenced pre-eminently by the centripetal migration 

 of the tentacles on to the exumbrella (comp. System, 1879, taf. xix., xx. pp. 302-306). 

 Whilst in other Craspedotae the tentacles usually retain their original position on the 

 umbrella margin, in the Narcomedusse they migrate from there up to the dorsal surface 

 of the exumbrella, towards the apex, taking with them, from their original insertion, part 

 of the umbrella margin, whose urticating ring is transformed into a centripetal umbrella 

 clasp (" peronium "), ( § 68, Pis. IX.-XI V., en). The original marginal coronal canal, 

 which lies on the inner side of the marginal urticating ring, follows the centripetal 

 processes of the latter, which forms the peronium in the exumbrella and edges the two 

 lateral margins of the peronium in the form of a double peronial canal (" canalis 

 peronialis," ck, Pis. IX. -XIV.). The two parallel double canals (which are only separated 

 by the peronium) open at the dorsal point of insertion of the tentacle, into the distal end 

 of the true radial canal, which is expanded like a pouch (Cunantha, Cunina, System, 

 taf. xix. figs. 1, 3). Whilst many Cunanthidas (the Cunoctanthida3) show this most simple 

 condition and are therefore connected immediately with certain Trachomedusas 

 (Geryonida^), in other Cunanthidse (Cunoctonidas) the distal part of each radial canal 

 bifurcates into two csecal pouches diverging distally, and these internemal lobe pouches 

 therefore lie in pairs between each two peronia and peronial canals (Cunarcha, PL IX. 

 figs. 2-4, Cunoctona, System, taf. xx. figs. 1-6). In the closely allied iEgmidse the 

 simple proximal part of the widened radial canals has undergone retrograde formation or 

 become merged into the periphery of the stomach, whilst the two lobe pouches which have 

 arisen from their distal part are developed into independent internemal gastral pouches, open- 

 ing immediately into the periphery of the stomach (sEginura, Pis. XIII., XIV.; JEgina, 

 System, taf. xx.). The double peronial canals, which open into the stomach between 

 each two pair of pouches, seem at first to be simple radial canals, connected by a simple 

 coronal canal at the umbrella margin ; this apparently simple coronal canal, however, 

 really consists of four or eight separate marginal canals (" canales marginales," cm); these 

 are completely separated by the distal ends of the peronia, and each marginal canal, along 

 with the inverted halves of the two contiguous peronial double canals, forms a horseshoe- 

 shaped arch canal. An arch canal opens by two separate ostia between each two peronia 

 into the gastral cavity. The entire coronal canal, when formed as in the iEginidas of four 

 or eight separate canals, is called the festoon canal (" canalis festivus," cf, Pis. XIII. , XIV.). 

 The Peganthidse (Pis. X.-XII.) present another modification. The radial canals are 

 merged in the central stomach or have undergone retrograde formation, so that the festoon 

 canal (or the modified coronal canal) opens immediately into the stomach and with twice 

 the number of openings than the number of arches composing the festoon canal ; each arch 

 opens by two gastral ostia (go). In the family of the Solmaridas the festoon canal is 



