XC1V THE VOYAGE OF H.M.S. CHALLENGER. 



Discomedusse, the group of the Typhloperise, or Ephyronise, without coronal canal, includes 

 first all the Cannostpmse (Ephyridse, Linergidse) and, secondly, half of the Semostomse 

 (Pelagidse, Cyaneidas). In these the sixteen coronal pouches always continue completely 

 isolated, whether they remain simple or become repeatedly branched. The tentacles 

 remain simple and unbranched in the Ephyridse (System, taf. xxvii., xxviii.) and Pela- 

 gidse (System, taf. xxxi.) each coronal pouch is, however, usually bifurcated into two lobe 

 pouches, which provide for the inverted halves of each two neighbouring canals ; the two 

 simple csecal lobe canals of each lobe therefore belong to two different adjacent marginal 

 lobes and remain completely separated by the (subradial) peronium. Consequently, 

 there are usually thirty-two csecal lobe pouches present, but this number may be 

 increased considerably by later division and the formation of secondary lobes. The 

 Lineragidse (System, taf. xxix.) and Cyaneidse (System, taf. xxx.), on the other hand, 

 are distinguished by distal ramification of the lobe pouches. Each lobe pouch sends out 

 numerous bifurcate or dendritic canals from their periphery ; these comport themselves like 

 the " dendritic velar canals " of the Cuboinedusse (PL XXVI. ), never form anastomoses, 

 and end everywhere with csecal branches at the periphery of the lobes (Pis. XXX., XXXL). 

 § 133. Cycloperise, or Ephyronise with annular canal. Whilst in the Typhloperise, 

 described above, the sixteen original coronal pouches and their distal ramifications remain 

 entirely separate, the second half of the Discomedusse is distinguished by the development 

 of a connecting coronal canal between the coronal pouches. Of the three sub-orders of 

 the Discomedusse, the Cycloperise or Ephyronise, with coronal canal, includes, first the 

 half of the Semostoruse (Flosculidse, Ulmaridae), and, secondly, the whole of the 

 Rhizostomse. It is clear from the ontogeny of the Cycloperise that they are derived 

 phylogenetically from the Typhloperise, and that their characteristic annular canal (" canalis 

 annularis," ck) has been developed secondarily, as a circular, peripheric anastomosis 

 between the originally separate, csecal coronal pouches. The Ephyrula larva of the 

 Cycloperise is so like that of the Typhloperise that they may be confounded together, and 

 is also furnished with sixteen simple, csecal, coronal pouches. In the course of their 

 metamorphosis, these pouches in the Cycloperise form lateral processes which grow towards 

 those of the neighbouring coronal pouches with which they enter into open anastomosis. 

 In this way the secondary annular canal of the Cycloperise (" canalis annularis ") is 

 formed ; it is analogous to, (not homologous with) the secondary circular canal (" canalis 

 circularis ") of the Craspedotse, but different from the coronal canal or primary ring- 

 canal of the Acraspedse (" canalis coronaris "). The latter lies at the proximal side of the 

 coronal pouches (between them and the four septal nodes), whilst the former Hes on the 

 distal side of the coronal pouches. Another important peculiarity of the Cycloperise 

 stands in direct correlation to the development of their annular canals ; the sixteen broad 

 coronal pouches of the Typhloperise are transformed in all Cycloperise into sixteen narrow 

 coronal canals, as the sixteen narrow subradial septal ridges between the pouches 



