14 THE CTENOPHORA 



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

 occur in the Ctenophora. 1 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 Anthomedusan are 



FIG. V. 



Ctenaria Ctenophora, Haeckel. A, side view ; B, two horizontal views, that to the left 

 representing the surface of the aboral hemisphere, that to the right a section passing nearly 

 equatorially. a, the right adradial ridges of nematocysts ; 6, mesogloea of the umbrella ; 

 c, circular muscle of the umbrella ; d, longitudinal muscles of the umbrella ; e, the gastral 

 cavity ; /, the sixteen oral tentacles ; g, the four perradial gonacls borne on the manubrium ; 

 h, the four perradial gastrovascular canals ; i, the eight adradial bifurcations of the preceding ; 

 k, ring canal at the umbrellar margin ; I, velum ; m, pocket-like cavities in the exumbrella 

 situated at the bases of the tentacles and lined -with nematocysts ; n, the tentacles ; o, the 

 upper moiety of the gastral cavity, called by Haeckel 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 Ctenophora have a solid axial cord of muscular 

 fibres derived from mesoblast. The sub-tentacular pouches of 

 Ctenaria correspond neither in position nor in their relations to 

 the tentacles to the tentacular sheaths of Ctenophores, and the 

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

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

 1 With one exception. 



