106 THE VOYAGE OF H.M.S. CHALLENGER. 



Siphon. — The single polypite of Eudoxia, or the manubrium of the sterile medusome, 

 always exhibits the same structure as in other Calyconectse. It is composed of four con- 

 stant parts : — (l) A short pedicle (sp) ; (2) a thick-walled, usually hemispherical, basi- 

 gaster, with masses of cnidoblasts (sb) ; (3) a dilated stomach, separated from the latter 

 by a pyloric valve, and usually provided with liver-stripes (sm) ; and (4) a very extensile 

 and contractile proboscis ; the latter opens through the mouth, which often exhibits four 

 or eight lobes. (Compare PL XXXII. fig. 8; PL XXXIV. figs. 9-11 ; PL XXXVIII. 

 fig. 12 ; PL XL. figs. 13, 14, &c.) 



Tentacles. — The single tentacle, which arises in each Eudoxia from the pedicle of the 

 siphon, has usually the structure which is characteristic of the alyconectae. The long 

 cylindrical and very contractile tubule is beset with numerous lateral branches or 

 tentilla, separated by equal intervals. Each tentillum is composed of three parts, a 

 slender pedicle, a reniform or ovate cnidosac, and a slender terminal filament. On the 

 structure of the cnidosac compare above, p. 97. 



Gonophores. — Each Eudoxia produces originally only a single gonophore, and this 

 fertile medusome is placed in the ventral part of the bracteal cavity of the sterile 

 medusome, before its siphon. In many species there is constantly found only a single 

 gonophore, and when this becomes detached, it is usually soon replaced by a secondary 

 or vicarious gonophore (" Ersatz-Geschlechts-Glocke"). But in some species usually two, 

 or even three, gonophores are found at the same time developing in one bracteal cavity ; 

 they are usually of different sizes and ages, one placed at the right of the siphon, the 

 other at its left (Pis. XXXIV, XLIL). 



Eudoxise with a single gonophore are always gonochoristic, either male or female. 

 When, however, two or three gonophores are developed simultaneously, then they are 

 either of the same sex (Eudoxise diclinicse, PL XLIL figs. 10, 14) or of different sexes 

 (Eudoxise monoclinicse, PL XL. fig. 14). 



Each single mature gonophore of the Eudoxidae is a well-developed quadriradiate 

 Medusa, without mouth and tentacles, with sexual cells in the wall of the manubrium 

 (spadix). The umbrella is rarely rounded, and without sharp edges, as in the gonophores 

 of Diplopkysa and Eudoxella; usually it is four-edged, prismatic or pyramidal; commonly 

 two dorsal edges are more strongly developed, and more prominent over the basal ostium, 

 than the two ventral edges. The apex of the umbrella is always prolonged into a beak- 

 shaped apophysis or apical horn, the pedicle by which the gonophore is attached to the 

 bracteal cavity. The quadriradial form of the umbrella in the single gonophore is 

 usually symmetrical (with equal right and left halves) ; but when two gonophores are 

 placed symmetrically on the two sides of one siphon, they are often modified by mutual 

 pressure, and the single umbrella assumes an asymmetrical (sometimes pentagonal) form. 

 (Compare p. 115, and PL XXXVI. figs. 12-25.) 



Compare on the development of the Eudoxidae above, pp. 100-102. 



