NARCOMEDUS^E — PEGANTHA. 447 



6, occasionally 7 to 8 sensory-clubs per lappet, each containing 3 to 5 concretions. These 

 sensory-clubs are placed upon bristle-bearing sensory-pads and linear otoporpae extend upward 

 over the exumbrella above each club about half the length of the lappet as in P. clara. Gonads 

 and gastrovascular system as in P. clara. 



Stomach, gonads, and canals deep opaque lemon-yellow, this color being due to minute, 

 highly refractive orange or yellow pigment granules confined to the ectoderm. Found on the 

 surface in the Humboldt current off Peru, South America. 



Bigelow discovered a development of larvae in this species which is analogous to the 

 process seen in Cunina probosadea. This development of larvae in P. smaragdma begins in 

 the gelatinous substance of the exumbrella near the margin of the gastric cavity. The ovum 

 is probably fertilized as was observed by Stshelkanowzeff in C. probosadea, but Bigelow did 

 not observe the process of fertilization. In the earliest stage recognized by Bigelow there is 

 a spherical cell which is destined to become the larva and which is inclosed by a vacuolated 

 cell destined to be the "nurse cell." The inclosed cell divides completely by mitosis and a 

 solid morula is formed, which remains inclosed by the nurse cell. This nurse cell may remain 

 undivided, but occasionally it divides once or twice and one or more of the resulting nuclei may 



degenerate. , 



The larva then penetrates through the entodermal wall of the stomach and enters the 

 gastric cavity, and during this process the nurse-cell disappears. The entoderm is formed by 

 secondary delamination as described by Metschnikoff in C. probosadea. Alter entering the 

 gastric cavity the larva elongates and resembles a small, detached tentacle with chordate 

 entoderm incased in a layer of ectoderm. A cavity appears in the entoderm near one end of 

 the larva and the ectoderm becomes thin at one side near this end ot the larva and the mouth 

 breaks through. The main part of the larva goes to form the first tentacle. A second tentacle 

 then develops 180 apart from the first, and then other tentacles develop irregularly. Larvae 

 with 4 or more tentacles often produce medusa buds at their aboral pole as is seen in Cunina 

 probosadea and C. prolifera (see text-fig. 320M. The bud may remain attached until !t 

 develops tentacles and a mouth at the pole opposite to that of attachment, or it may be set 

 free as a mere sac. Two buds may be developing at one and the same time. The bud-larvae 

 after being set free are similar in all respects to those developed directly from the egg. The 

 developing medusae flatten out, become about 3 mm. wide with thin, gelatinous substance, 

 10 to 12 tentacles, and 2 to 3 sensory-clubs per marginal lappet. No otoporpx. The lappets 

 are short and broad with indistinct incisions between them. The stomach is a simple sac 

 with a circular entire margin, no marginal canals, and a round mouth-opening. The gonads 

 appear to develop diffusely in the ectoderm over the subumbrella wall ot the stomach. I he 

 medusa; swim actively within the stomach of their parent, through whose mouth they escape 

 to lead an independent existence. In their characters they resemble the genus Solnians. 



Family jEGINID^E sens. ampl. 



Cunmthide+ Mginida, Haeckel, 1879, Syst. der Medusen, pp. 310, 334. 



Narcomedusae in which the stomach-margin is not plain and circular, but gives rise to 

 outwardly projecting, marginal pouches. 



REMARKS ON THE GENERA OF THE ^GINIDiE. 



Cunantha: "Cunantha" prnnigenia and C. p*».f*j Haeckel, .879, PP- 3'4. 3>5- "<= apparently larval stages of Mgina. Cun- 



antha striata Haeckel may possibly become mature in condition postulated for Cunantha r 

 £ e ina- These medusa develop through a "Cunantha" stage and generally become mature in Mgtna stage, sens, stnct., with 8 



adradial stomach-pouches; but a few acquire 16 peripheral stomach lobes before attaining maturity. 

 Solmundella: This genus is derived from Mgina by disappearance of half of its tentacles, reducing them from 4 to 2. 

 Hvdroctena: Distinguished bv its well-developed apical sense-organ and gelatinous axial cores of tentacles. No peromal strands, 



although basal sheaths of tentacles may be remnants of peronial furrows. This form may be derived from Solmunddla. 



The larval Solmunddla has a simple, ciliated, apical plate. 

 Cunoctantha: Closely related to Cunina, but is 8-rayed. 



Cunoctona: " Cunoctona" of Haeckel is only a stage in ontogeny of Mginura. _ 



Mginopsis: Derived from Mginura by disappearance of 4 interradial tentacles. Mginops.s bears same relation to Mg.nura 



as Solmundella does to Mgina. 

 Cunina: Closely related to Cunoctantha but has more than 8 rays. 

 Solmissus: Closely related to Cunina but it is without otoporpa or marginal loop-canals. Otoporps are always present and 



loop-canals may be present in Cunina. 

 Cunissa- "Mginodorus" Haeckel is only a special case of Cunissa in which there are 16 tenacles. 

 Mginodiscus: This is apparently derived from an ^ginodorus-like medusa by disappearance of every alternate tentacle. 



