HYDRO-MEDUSA. 75 



certain medusa, a Pelagia, develop precisely in this way.* If, 

 then, by some process, that part of the Ephyra of Pelagia in 



which may be traced even to the tips of the feelers (I), and very easily followed 

 all over the club-shaped ends (p 1 ) of the fertile individuals. 



In order to understand the true character of the latter forms, we must study 

 the structure of the smooth, club-shaped individuals (II). This clubbed termi- 

 nation of the stem is simply an expansion of the latter in such a way that the 

 outer wall (o) separates from the inner one (in), and leaves a space (c) between 

 the two. Within this space, and consequently around the inner wall which pro- 

 jects into it like a proboscis (pr 1 ), the eygs (eg) are developed. This is plainly 

 then a reproductive organ raised on a stem identical in character with that which 

 supports the feeding hydra (I). 



Did the colony consist merely of a single feeding hydra and a group of fertile 

 ones attached to it, for instance, just as it appears to be in this illustration, 

 it would be no difficult matter to decide that the feeder is the individual centre, 

 and that the fertile ones are its reproductive organs, which are attached to it by 

 elongated pedicels, in the same way that the reproductive organs, or meduso- 

 genitalia, of Tubularia (chapter xiv.) are joined to the head. The relationship 

 of the organs in question is the same in Tubularia as in llhizogeton, with only a 

 difference in degree, which is bridged over by the intermediate forms of Coryne 

 (fig. 42) and Clava, in which the meduso-genitalia are more or less scattered 

 along the shaft of the hydra, which represents in itself both the feeder and the 

 reproducer. But the character of the individuality of Rhizogeton is complicated, 

 inasmuch as it is a compound of several feeders and numerous reproducers, so 

 that one could not tell to which of the former any one of the latter belonged. 



As I said before, the nature of some of the fertile forms cannot be understood 

 without a close study of the smooth, club-shaped (fig. 38, II) ones. The rela- 

 tions of the walls of the latter I have already pointed out, and it now remains to 



* There happen to be two well-authenticated instances on record: one in re- 

 gard to the Steganophthalmic, and the other respecting the Gymnophthalmic 

 Medusae. In both cases the discoverers traced the development of the medusa 

 directly from the egg, and thus put the facts beyond a doubt. See Krohn, 

 " Ueber die friihesten Entwickelungsstufen der Pelagia noctiluca" Miiller's 

 Archiv, 1855, p. 491, Taf. xix., and Claparede, " Ueber geschlechtliche Zeugung 

 von Quallen durch Quallen," Zeitsch. fur. wissenschaft, Zob'L, 1860, vol. x. p. 401, 

 Taf. xxxii. figs. 1, 2, 3. The observations of Gegenbaur, J. Miiller, Fritz Miiller, 

 and L. Agassiz, upon the development of medusae without an intermediate hydra- 

 phase, are open to doubt, inasmuch as the young were not traced from the egg ; 

 and therefore no one can say that they did not arise by budding, either from a 

 hydra-form, or from the internal surface of the digestive cavity of a medusa. 



