84 MEDUSA OF THE WORLD. 



This family is of such interest that we devote more than the usual space to its consider- 

 ation. Haeckel, 1879, classifies it as a family coordinate with the Codonidae, but Hartlaub, 

 1887, showed that the genus Cladonema had an encircling gonad as in the Codonidae. The 

 medusa; are, however, highly specialized, both in respect to their anatomy and their mode of 

 life, and they are undoubtedly derived from some more simply-organized medusae among 

 the Codonidae. The hydroid of Cladonema is a StanriJia, and is closely related to Syncoryne, 

 the hydroid of Sarsia. 



CHARACTERS OF THE FAMILY CLADONEMID^. 



Anthomedusae with feathered or branched marginal tentacles, and with four or more 

 simple or branched radial-canals. The gonads may be ring-like and encircle the stomach, or 

 they may be more or less separated so as to be interradial or adradial, or developed in a spec- 

 ialized brood-pouch above the stomach. 



Hartlaub, 1887, and Perkins, 1902, show that in the genus Cladonema the genital products 

 are developed over the entire gastric portion of the manubrium and the gonads are not con- 

 fined to restricted meridians, as was believed to be the case by Haeckel. Hartlaub found that in 

 Cladonema radiatum of the Mediterranean the genital products begin to develop in the ento- 

 derm. This species exhibits a successive hermaphroditism, although either sperm or ova may 

 precede. Perkins, however, in his study of Cladonema pcrkinsn of the Bahamas, found that 

 the genital products were developed in the ectoderm of the manubrium, and he failed to find 

 sperm or ova in the entoderm. 



In Eleutheria, Hartlaub, 1 886, 1887 (Zool. Anzeiger), showed that the genital products 

 are developed exclusively in the ectodermal lining of a peculiar brood-pouch above the stomach, 

 and that the medusa is hermaphroditic. The brood-pouch is derived from the ectodermal 

 layer of the bell-cavity and is not connected with the stomach of the medusa, but communi- 

 cates with the bell-cavity by means of 6 interradial-canals. 



Hartlaub, 1887, divides the Cladonemidae into two groups, one with and the other without 

 an apical brood-sac above the stomach. As this brood-sac is highly variable in its develop- 

 ment, some specimens of Eleutheria apparently failing to develop it and, moreover, as it is a 

 character which develops during the growth of the medusa and is not found in the young 

 animal, it would seem that Haeckel's classification of the Cladonemidae, based as it is upon 

 the possession of constant characters, is to be preferred. Moreover, as has been shown by 

 Giinther, 1903, we can not yet state that the brood-pouch of other genera of Cladonemidae is 

 similar in structure to that of Eleutheria. 



As is well known, Haeckel, 1879 (Sitzungsber. Medicin. Naturwiss. Ges. Jena; see also 

 Chun, 1880, Ctenophoren des Golfes von Neapel), drew an ingenious comparison between 

 Ctenaria and the Ctenophorae, and concluded that the Ctenophorae might have been derived 

 from some form of Anthomedusa. Ctenaria appears to resemble the Ctenophorae in its 2 

 feathered tentacles, 4 bifurcated radial-canals, and in a peculiar sheath at the base of each 

 tentacle. However, Hartlaub's discovery that the brood-pouch in the closely-related Eleu- 

 theria is of ectodermal and not entodermal origin makes it appear that the resemblances 

 between Ctenaria and the Ctenophorae are of the nature of a mere parallelism and not indic- 

 ative of a genetic relationship. Haeckel compared the 8 adradial longitudinal lines of 

 nematocysts upon the exumbrella of Ctenaria with the 8 rows of ciliated combs in the 

 Ctenophorae. An even more remarkable case of convergence is shown by Kofoid, 1905 

 (Bull. Mus. Comp. Zool. at Harvard College, vol. 46, p. 163, i plate), in the case of the 

 Cystoflagellate, CraspeJotella, which is bell-shaped and provided with a well-developed velum, 

 the walls of which are contractile so that the mode of locomotion is similar to that of a medusa. 

 There is thus an external similarity of form between this protozoan and a medusa offering an 

 instance of convergence of a most striking character. Another remarkable instance of conver- 

 gence is that of the pelagic holothurian Pelagothuria natatrix, which bears a close resemblance 

 to a medusa (see Mem. Mus. Comp. Zool. at Harvard College, vol. 17, 1894). I believe also 

 that the bell of the Narcomedusa? is not homologous with that of the Anthomedusae and 

 Leptomedusae, but is a mere outgrowth from the walls of the actinula larva. 



