386 APPENDIX. 
sexual generation, vol. i. p. 192), from adhering hydroid polyps 
(2,3). These latter, however, originate out of the fructified eggs 
of the medusez (therefore by sexual generation, vol. i. p. 195). 
Hence the non-sexual, adhering generation of polyps (I., IIL, 
V., etc.) regularly alternates with the sexual, freely swimming 
generation of meduse (IL, IV., VI., etc.) This alteration of 
generation can only be explained by the Theory of Descent. 
The same remark applies to a kindred form of propagation, 
which is still more remarkable, and which I discovered in 1864, 
near Nice, in the Elephant-jellies (Geryonida), and called allao- 
gony, or alleogenesis. In this case two completely distinct forms 
of medusa are descended from one another; the larger and more 
highly developed generation (11), Geryonia, or Carmarina, is six- 
rayed, with six foliated sexual organs, and six very movable 
marginal filaments. From the centre of its bell-shaped cup, like 
the tongue of a bell, hangs a long proboscis, at the end of which 
is the opening of the mouth and stomach. In the cavity of the 
stomach is a long, tongue-shaped bunch of buds (which on 
Plate VII. (7) is extended from the mouth on the left like a 
tongue). On this tongue, when the Geryonia is sexually ripe, 
there bud a number of small meduse. They are, however, not 
Geryonix, but belong to an entirely distinct but very different 
form of medusa, namely, to the genus Cunina, of the family of 
the Aginida. This Cunina (12) is very differently constructed ; 
it has a flat, semi-globular cup without proboscis, consists in 
early life of six divisions, later of sixteen, and has sixteen bag- 
shaped sexual organs, and sixteen short, stiff, and strongly curved 
tentacles. A further explanation of this wonderful alloeogenesis 
may be found in my “Contributions to the Natural History of 
the Hydromeduse.” (Leipzig, Englemann, 1865), the first part 
of which contains a monograph of the Elephant-jellies, or 
Geryonida, illustrated by six copper-plates. 
Even more interesting and instructive than these remark- 
able relations are the vital phenomena of the Siphonophora, 
whose wonderful polymorphism I have frequently spoken of, 
and described in a popular manner in my lecture on “ Differentai- 
