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



larger basal half encloses the siphosome, which proceeds through its lower aperture ; the 

 two halves are separated by the apex of the trunk, from which arise also the pedicles of 

 the two nectophores (fig. 4b, a ; fig. 7, np). The two ventral wings of the larger basal 

 nectophore (fig. 4b) embrace the two opposite ventral wings of the smaller apical necto- 

 phore (fig. 4a) so completely that the lateral sides of the hydrcecial canal are perfectly 

 closed (fig. 3, apical view). 



Siphosome (fig. 1). — The common trunk of the cormus is a cylindrical tube of the 

 highest contractility, and in the contracted state is very short and partly hidden in the 

 hydrcecial canal ; in the fully expanded state it attains a length of more than two feet 

 and offers a splendid aspect, the numerous cormidia (forty to fifty or more) being 

 separated by equal intervals, each giving off a bright yellow contractile siphon, and a 

 long tentacle with numerous tentilla, the latter armed with yellow cnidosacs. 



Cormidia (PI. XXXII. ). — Each cormidium is a eudoxome, composed of two medusoid 

 persons, a sterile medusome (siphon with bract and tentacle), and a fertile medusome (the 

 gonophore). Sometimes two gonophores occur in the same group. The gonophores in 

 the proximal part of the trunk are usually female, those in the distal part male ; but 

 sometimes both sexes alternate rather regularly. The cormus is therefore monoecious. 

 The gonads are very small ; often perhaps they do not become ripe until the Eudoxise 

 have become detached from the stem, but usually they seem to ripen sessile on the 

 trunk. Some free-swimming Eudoxise, belonging to the genus Eudoxella (Genus 11a) 

 are so similar to the sessile Eudoxome of this species of Praya, that I suppose they 

 have been detached from a species of this genus. 



Bract (PI. XXXII. fig. 8, b ; fig. 9).— The bract or hydrophyllium (the umbrella of 

 the sterile medusome) somewhat repeats the kidney-form of the nectophores. It 

 attains a length of 10 to 12 mm., a height of 8 to 10 mm. Its jelly-wall is very thick 

 and soft, mainly in the rounded apical half. The basal half is deeply excavated, and its 

 thinner-walled cavity, corresponding to the subumbrella (w), encloses the siphon with its 

 tentacle, and the gonophore. The convex exumbrella is rounded and smooth all round, 

 and at its basal margin presents three deep sinuses or incisions, two paired lateral and one 

 odd dorsal (fig. 9). The trunk of the siphosome (fig. 8, a) passes through the two lateral 

 incisions, while the tentacle (fig. 8, t) steps out through the dorsal incision. Two lateral, 

 nearly quadrangular lobes, comparable to the two buccal valves of a helmet, are separated 

 by those sinuses. 



Canals of the Bract (figs. 8, c, 9, c) — Each hydrophyllium must be regarded as the 

 reduced umbrella of a Hydromedusa, and still possesses the four radial canals, char- 

 acteristic of the latter. A short peduncular canal or apical vessel (figs. 8, 9 ca), goes from 

 the trunk (a) to the apical part of the subumbrellar cavity, gives off a short spindle- 

 shaped caecum (phyllocyst), and four divergent, irregularly bent canals, two odd sagittal 

 and two paired lateral. The odd ventral canals (cv) forms an S-shaped loop in the solid 



