14 



THE CTENOPHORA 



essential difference, and, for the rest of it, nematocysts do not 

 occur in the Ctenophora.^ The sub-umbrella cannot be compared ■' 

 either in its development or in its adult relations to a stomodaeum. ■ 

 There is a superficial resemblance between the gastro-vascular 

 system of the two forms, but even if we pass over the absence 

 of anything representing the manubrium and oral tentacles in 

 Ctenophora, we find an essential difference in that the endoderm 

 lamella, in which the radial canals of the Anthoniedusan are 



I'Ki. V. 



Cteiiarla ctenojihont, Ilaeckcl. A, side view ; H, two horizontal views, that to the left 

 representing the snrfiice of the aboral heniisi)liere, that to the right a section jwissing nearly 

 equatorially. a, the right acliadial ridges of nematocysts; h, iiiesogkva of the unihrella ; 

 c, circnlar muscle of the umbrella ; rf, longitudinal muscles of the umbrella ; c, the gastral 

 cavity ; /, the sixteen oral tentacles; ri, the four i)erradial gonads borne on the manubrium ; 

 h, the four jierrailial gastrovascnlar canals ; i, the eight adradial bifurcations of the preceding ; 

 A', ring canal at the umbrellar margin ; /, velum ; hi, pocket-like cavities in the exninbrella 

 situated at the Imiscs of the tentJich-s ancl lined with nematocvsts ; », the tentacles; o, the 

 ui>per moiety of the gastial cavity, called by llaecki-1 the infundibulum. 



hollowed out, is entirely unrepresented in the Ctenophora. Nor 

 is there any ring canal in the latter group. The tentacles of 

 Ctenaria are lined by endoderm, their musculature is epithelial; 

 the tentacles of Ctcno])h()ra have a solid axial cord of muscular 

 fibres derived from mosol)last. Tiic sub-tentacular pouches of 

 Ctenaria correspond neither in ])osition nor in their relations to 

 the tentacles to the tentacular sheaths of Cteno))hores, and the 

 existence of such nematocyst pouches, as well as the existence of 

 only a single pair of jierradial tentacles, is paralleled in other 

 ' With one exception. 



