ON THE AFFINITIES OF THE FAMILY OF THE MEDUSJi 2/ 



68. The ovarium of the Pluniularia above mentioned (65), com- 

 mences as a dilatation of the apex of its pedicel, which again is a 

 process of the common stem. It then becomes lenticular with a horny 

 outer wall, glassy and transparent externally, but internally coloured 

 by pigment masses. Internally it has an oval cavity communicating 

 with that of the stem and lined by a distinct membrane, fig. 45. 

 Between the two membranes is a thick layer of ova, more or less oval 

 in shape, and about TjJ-ijth of an inch in diameter, with a germinal spot 

 about -J 4-^ooth of an inch in diameter, seated in the middle of a clear 

 space about twice that size, which doubtless represents the germinal 

 vesicle. 



69. The account given by Lowen of the generative organs of 

 Campanularia differs considerably from the foregoing. After all, 

 however, his " female polypes " may be nothing more than ovaria 

 similar to those of Dipliyes or Coryne, but having the production of 

 tentacles from the margin carried to a greater extent than in the 

 latter. If this be a correct explanation, the idei promulgated by 

 Steenstrup, that there is an " alternation of generations " among the 

 Sertularian Polypes, must be given up. 



70. In Hydra} the ova are developed in similar processes of the 

 lower part of the body. But among the Hydroid Polypes the ovaries 

 of Coryne, Syncorine and Corymorpha, as described by Sars, Lowen 

 and Steenstrup, are most interesting. They commence as tubercles 

 of the stem, afterwards become bodies, precisely resembling the ovaria 

 of the Diphydse, and finally (fig. 42) detaching themselves develope 

 regular tentacles from their margin. The ova are formed between the 

 two membranes of the inner sac- 



71. What has now been advanced will perhaps be deemed evidence 

 sufficient to demonstrate, — ist, that the organs of these various 

 families are traceable back to the same point in the way of develop- 

 ment ; or 2ndly, when this cannot be done, that they are connected 

 by natural gradations with organs which are so traceable, in which 

 case, according to the principles advanced in 57, the various organs 

 are homologous, and the families have a real affinity to one another 

 and should form one group. 



1 M. Dujardin, Annales des Sciences Naturelles, November 1845, states on the authority 

 of Ehrenberg, Corda and Laurent, that the ova of the freshwater Polype are "produits dans 

 I'epaisseur meme du tissu sans ovarie ni ovule prealable." 



2 "The axis of the bell is occupied by a membranous sac, which is a prolongation of the 

 nutritive canal, and answers to the alimentary cavity of the alimentary Polypes. The ova 

 are developed in regular series in the interval between this alimentar)' capsule and the parietes 

 of the outer sac, in an intermediate membranous sac, distinguished by its yellowish brow n 

 colour."— Cuvier, Lejons d'Anat. Comparee, t. viii. Organs de Gene'ration des Zoophytes, 

 p. 860. See also Duvernoy, Annales des Sciences Naturelles for November 1845. 



