42S MEDUSAE OF THE WORLD. 



Order NARCOMEDUSjE Haeckel, 1879. 



&ginidtr, Gegenbaur, 1856, Zeit. fur wissen. Zool., Bd. 8, p. 259. 



Thalassanthece, Agassiz, L., 1862, Cont. Nat. Hist. V. S., vol. 4, p. 167. 



Narcomedustf, Haeckel, 1879, Syst. der Medusen, p. 299. — Maas, 1897, Mem. Museum Comp. Zool. at Harvard College, vol. 



23, p. 27; 1905, Craspedoten Medusen der Siboga Expedition, Monog. 10, p. 64; 1906, Fauna Arctica, Bd. 4, Lfg. 3, p. 



496. — Vanhoffen, 1907, Zool. Anzeiger, Bd. 32, p. 175; 1908, Wissen. Ergeb. deutsch. Tiefsee Exped., Bd. 19, Heft 2. — 



Bigelow, H. B., 1909, Mem. Museum Comp. Zool. at Harvard College, vol. 37, p. 47. 



CHARACTERS OF THE ORDER NARCOMEDUS^E. 



Veiled medusae with marginal sensory-clubs containing concretions of entodermal origin 

 and with bell-margin cleft into lappets. The web-like velum bridges over these clefts between 

 the lappets and also projects as a diaphragm beyond their outer margins, in such manner as 

 to form an annulus which partially closes the opening of the bell-cavity. 



There are free sensory-clubs, with entodermal concretions upon the margins of the lap- 

 pets. These sensory-clubs arise from pad-like, bristle-bearing ectodermal thickenings, and a 

 bristle-bearing tract of ectodermal cells may or may not extend up the sides of the exumbrella 

 above each sensory-club. Haeckel calls these tracts "otoporpae." 



The tentacles project stiffly from the sides of the bell at the upper ends of the clefts between 

 the lappets. A strand of ectoderm, called the peronium, extends along the groove of each cleft 

 to the ventral side of the base of the tentacle, where it becomes thickened, forming a cushion- 

 like pad beneath the tentacle and serving apparently for its support. The tentacles are* 

 always solid, with their entodermal cores composed of a single, axial row of disk-like, chordate, I 

 vacuolated cells. These axial cores of the tentacles are sheathed in ectoderm and penetrate 

 inward through the gelatinous substance of the bell to the margin of the central stomach. 

 Indeed the axial-core of each tentacle is continuous with the entoderm of the margin of the 

 stomach, while its ectoderm is continuous with that of the exumbrella. The tentacles often bear 

 bristles, especially near their tips, where they are usually quite conspicuous in young medusae. 

 A single row of nematocyst-capsules often extends along the abaxial line of each tentacle. 



The central stomach is a lenticular space, bounded outwardly by the insertions of the 

 tentacles. The subumbrella floor of the stomach is usually quite flat, although occasionally 

 it is conical. The mouth is usually a simple, round opening, although in a few species there 

 are 4 lips and an elongate throat-tube. The margin of the stomach may be simple and circular, 

 or it may display peripheral pouches, due, in Cunoctantha at least, to interradial fusions of the 

 stomach walls dividing the originally circular stomach-cavity into spoke-like outpocketings. 

 Saccules in the intertentacular radii may also project in the form of pouches from the sub- 

 umbrella floor of the stomach. In forms having saccules or pouches projecting downward 

 from the subumbrella floor of the stomach we find that the central cavity of each sac is 

 filled by a projecting plug of gelatinous substance which extends downward from the aboral 

 wall of the stomach. 



A marginal ring-canal system may or may not be present and is often variable in its 

 development even in different individuals of one and the same species. When present the 

 ring-canal system consists in a loop around the margin of each lappet and thus the ring-canal 

 is separated into as many loops as there are lappets. Each loop bends between two adjacent 

 pairs of tentacles, extending outward from the stomach-cavity along one side of a tentacle 

 down along the same side of the peronium of this tentacle and upward along the side of the 

 adjacent peronium and its tentacle into the central stomach-cavity of the medusa. 



The gonads are developed in the ectoderm of the subumbrella under the central stomach 

 or upon its subumbrella pouches. The gonad may be ring-like or more or less isolated upon 

 separated stomach-pouches. The ring-muscles of the velum and subumbrella are very power- 

 ful and swimming is accomplished mainly through their action. 



The development has been studied by J. Miiller, Gegenbaur, McCrady, F. Miiller, F. E. 

 Schulze, Metschnikoff, H. V. Wilson, Korotneff, Maas, Brooks, Woltereck, Stschelkanowzeff, 

 H. B. Bigelow, and others. In some cases, as in Solmundella, the egg develops into an actinula 

 larva and this becomes directly transformed into a medusa by the outgrowth of the bell from 

 the sides of the body between the tentacles. The tentacles of the actinula become those of the 

 medusa and the bell grows outward between and beyond the tentacles so that we can not 

 assert that the tentacles have migrated upward from the bell-margin, for the bell has actually 



