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 



Fu:. V. 



Ctenaria ctenoplwra, 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. o, the right adradial ridges of nematocysts ; b, MMOgkeB of the umbrella ; 

 c, circular muscle of the umbrella ; d, longitudinal muscles of the umbrella ; c, the gosfcral 

 cavity ; /, the sixteen oral tentacles; g, the four perradial gonads Korno or. \},>- laanubrHun : 

 h, the four perradial gastrovascular canals ; t, the eight udradial bifurcations of th- pm-flm:. 

 k, ring canal at the utnbrellar margin ; I, velum ; m, jocket-lik ca . .- it. the exuinbrellu 

 situated at the bases of the tentacles and lined with iimiuiovxst* : , tin- tentacles ; o, ih-- 

 upper moiety of the gastral cavity, called by Haeckrl tin- hifund'ibuUiin. 



hollowed out, is entirely unrepresented in the Ctenophora. Nor 

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

 Ctenaria are lined by endoderm, their musculature is epithelial . 

 the tentacles of Ctenophora IIUVL a solid axial cunl of musciila 

 fibres derived from mesoblast. The sub-tentucular pouches of 

 Ctenaria correspond neither in portion nor in their relations ' 

 the tentacles to the tentacular sheaths of Ctenophorcs, and the 

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

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

 1 With one exception. 



