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



endoderm cells which authenticate their origin (cathammal plate, § 101). The marginal 

 coronal canal (cc), which connects the four radial canals at the umbrella margin, does not 

 appear to be the marginal part of the originally simple gastral space (of the Hydropolyps) 

 which remains open, but to have arisen from the distal ends of the radial canals which 

 remain open, being connected by marginal processes (hence the secondary coronal 

 canal). This typical primitive form of the coronal intestine of the Craspedotse is 

 subject to varied modifications, of which some (Narcomedusse) are so like the pouch 

 corona of the Acraspedse that they may be confounded with it (" convergent selection "). 

 § 123. Radial canals (" canales radiales," cr). In the majority of Craspedotae we 

 only find four perradial canals, which open into the coronal canal at the insertion of the 



Fig. N. Octorchis germanica (Leptomedusse, Eucopid*). 



Profile view, (ug) Gelatinous umbrella, [us) Solid gelatinous peduncle of the stomach, (v) Velum. 

 (to) Velar marginal vesicles, (tp) Perradial tentacles, (ti) Interradial tentacles. («') Distal testis 

 (on the subumbrella). (s 2 ) Proximal testis (on the oesophagus), (cp) Perradial canals. (</) Stomach. 

 (al) Oral lobes. 



four primary tentacles. They are usually very narrow and cylindrical, more rarely flattened 

 like a ribbon (in some Tiaridse, Geryonidse, Narcomedusse). There are rarely six canals 

 instead of four (in part of the Cannotidse and Geryonidse, System, taf. ix. figs. 6-9 ; 

 taf. xviii. figs. 7, 8). In some families eight canals are constant, as four interradial 

 secondary canals are developed supplementarily in the middle between the four perradial 

 (Pis. III.— VIII. ; Melicertidse, Octocannidse, Trachynemida?, Aglauridse, System, taf. viii., 

 xvi., xvii.). On the other hand we rarely find eight adradial canals, which have arisen 

 from basal bifurcation of the four perradial (Ctenaria, Cladonema, Dendronema, System, 

 taf. vii.). In the iEquoridse the number of the radial canals rises from 8 to from 



