HYDROIDA. 



241 



Fiji. 139. 



The tentacles (fig. 139, t) of the Scyphostoma of Aurelia (p. 

 70, fig. 37) seem to be in a single circle, whereas 

 they have the same arrangement as those of the 

 corona of Tubularia. The internal organization 

 of the Scyphostoma, as well as the mode of de- 

 velopment of its tentacles, has an unquestion- 

 able relation to right and left. At a very early 

 period the interior is subdivided into four longi- 

 tudinal, partially separated compartments, by the 

 projection of four equidistant, thick semi-parti- 

 tions. In full-grown individuals (fig. 139) these semi-partitions 

 (fig. 140, a,) extend from the base of the tentacles (t, t 1 ) half- 

 way to the bottom of the general cavity 

 (//<). On account of their transparen- ,, je/fj^ 

 cy, they have been mistaken for tubes, 

 and the fold (6, b l ) opposite each one of 

 ,them, in the muscular layer, has also 

 been erroneously described* as a chan- 

 nel in which the fluids circulate ; but each 

 of the first (a) is a solid, jelly-like mass Fig. 140. 



standing out like a pilaster, and the second (b) is so doubled upon 

 itself longitudinally as to present a quadruple contour, like the 

 two outer and two inner profiles of a tube. The thickness of 

 the walls at the base (d) of the circle of tentacles has also the 

 appearance of a circular tube into which the four supposed lon- 



34). o, the base ; m, the partially extended proboscis, encompassed by the ten- 

 tacles (<) ; d, the incipient formation of the discs of the Ephyra, foreshadowed by 

 transverse rings. Original. 



Fig. 140. An end-view of the head of fig. 139. 20 diam. t, fl, the tenta- 

 cles ; p, p 1 , the margin of the four-sided proboscis ; gc, the cavity of the body ; 

 ac, the bottom of yc, where the cavity (,s) of the stem opens ; d, the periphery 

 of gc, at the base of the tentacles ; a, the semi-partitions, or pilasters ; c, the 

 depression immediately over the anterior end of each pilaster, which appears like 

 an aperture; b, ft 1 , the longitudinal fold. Original. 



* See Frantzius on the Scyphostoma of Cephea borbonica, in Zeitsch. fur 

 wissenschaft. Zoblogie, June, 1852. Also Gegenbaur upon the same, in his 

 Generationswechsel, 1854, Taf. n. fig. 34. 



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