312 HYDROIDiE. Part IV. 



{Figs. 6, a b, and 1, a b c) near the base of the cup appears to be a separate 

 layer from the wall on which it rests, and is composed of two strata; the upper 

 one of which extends from the edge of the median aperture to the wall of the 

 calycle, and (c^) along the inner face of the same, toward its mouth, Avhile the 

 lower, or abactinal side of the semi-partition, projects from the edge of the central 

 aperture, in the form of a narrow rim {b), toward the base of the calycle, and 

 also extends along the inner face {c^) of the latter into the pedicel. In an 

 empty calycle {Fie/. 6) there may be observed, with a low power, a row of dots 

 (a) along the outer edge of the partition; these, when more highly magnified 

 {Figs. &' and 7, a), prove to be the papillas of a fringe which projects from the 

 exterior margin, and is a direct continuation of the same. It is quite evident 

 that these papillse have to do with the attachment of the hydra to the calycle, 

 although they would not seem to be absolutely necessary, as they are not present 

 in Obelia commissuralis and some other allied species. The space between the 

 partition and the base of the calycle is twice as broad as deep, and but little 

 broader than the proximate point of the pedicel. 



The reproductive calycle stands on a four or five-ringed pedicel {Figs. 15 and 

 18, k), which rises from the base of each hydra pedicel, just without the fork; 

 its shape, when mature {Fig. 18), is elongate oval, and opens by an aperture no 

 larger than the entrance from the pedicel at its base. It is about four times 

 longer, and one half broader than the calycles of the hydraj. The wall is of the 

 same thickness throughout, and equal to that of the base of the hydra calycle. The 

 sterile hydra (PI. XXX. Figs. 4 and 5) has at least thirty tentacles, and it appears 

 to be essentially the same in structure with that of the genus Obelia. The axis 

 {Fig. 15, {i y) of the reproductive hydra bears the same relations to the calycle 

 {k) as in Obelia and Eucope, but the medusae {h^), although developing in exactly 

 the same manner, do not become so highly complicated, nor are they ever freed, 

 to live an independent life, but reproduce their kind through planula\ and then 

 wither. 



Embryology. Proles medusoidea. — The highest degree of development to which 

 the medusa attains, corresponds to the very early stage of those medusae which 

 become free; in fact, the medusa of this species is nothing more than a double- 

 walled hernia (PI. XXX. Figs. 15, h\ 16, and 17, h' li'; PL XXXI. Figs. 2, 5, 5% 

 6, 6'', 7, and 8, U h% with a space between its outer and inner walls, in which 

 either the egg (PI. XXX. Figs. 15 and 16, ae) or the spermatic particles {Fig. 17, 

 ae) are developed. In the female medusa {Fig. 15, A') the egg {ae) begins to 

 develop before the inner wall of the medusa has risen above the level of the 

 axis. Presently, however, the inner wall also projects, and forms an elevated floor 

 upon which the egg rests (see the upper ae, Fig. 15); and, finally, the two walls, 



