450 



MEDUSAE OF THE WORLD. 



medusa has 8 large stomach-pouches, 2 in each intertentacular quadrant. The medusa 

 usually becomes mature in this (Mgina, sens, str.) stage, but occasionally each of the 8 main 

 pouches develops a median peripheral notch, thus giving 1 6 shallow, outer pouches. The 

 peripheral stomach-pouches thus increase by successive bifurcations, commencing with a 

 hypothetical larval stage with only 4 simple pouches in the tentacular radii. 



Vanhoffen, 1908, found that one of the Pacific species of Mgina usually has 5 tentacles, 

 and that the number ranges from 4 to 6. Bigelow, 1909, found a medusa which he calls 

 Mgina alternans which has 4 interradial, marginal stomach-pouches. It is possible that 

 the interradial cleft usually seen has become secondarily obliterated through coalescence of 

 the adjacent pouches, but of this we know nothing. 



The genus is thus distinguished chiefly by its having 4 to 6 tentacles and 4 to 6 peronial 

 strands, not by the precise condition of its peripheral stomach-pouches. In common with 

 other Narcomedusze, the peripheral canal-system is very variable in its development and often 

 degenerates or is wanting. When present, the loop-canals are in the intertentacular sectors, 

 a canal arises from the stomach on either side of each tentacle and extends down on the same 

 side of the peronium to the margin, where it continues through the sector to ascend along the 

 sides of the adjacent peronium and tentacle. In " Solmundus" Haeckel there are no peronial 



canals. 



Haeckel widely separates medusae with otoporpae from those without these minute, bristle- 

 bearing exumbrella tracts above their sensory-clubs, but this slight difference may probably 

 be best regarded as of specific rather than of generic value. 



The peronial furrows are often partially or wholly closed over, leaving the peronial strands 

 buried within the gelatinous substance of the bell. 



Maas. 1904, pp. 33, 35, considers Mginopsis Brandt, to be an advanced stage of Mgina 

 Eschscholtz, basing this opinion upon the more advanced subdivision of the peripheral stomach- 

 pouches of Mginopsis; but he appears to overlook the fact that in Mgina there are only 4 to 6 

 peronial strands, whereas in Mginopsis there are 8, and the two genera are therefore quite 



Synopsis of the Species of JEgina* 



Shape and size of bell in mm. 



Length of the tentacles in 

 terms of bell-radius (r). 



Number and character of the 

 marginal sense-organs. 



Character of mouth. 



Character of stomach-pouches 



Peronial loop-canals. 



Gonads. 



Color. 



Where found. 



M. citrca Eschscholtz, 1829= 

 jEgina rosea Eschscholtz. 



Hemispherical. 20 to 50 wide. 



2 to 16 in each interperonial 

 quadrant. 



A simple, round opening. 



8 cleft so that there are 16 shal- 

 low peripheral lobes. 8 main 

 pouches are adradial and ex- 

 tend about half the distance 

 from central stomach to bell- 

 margin. 



Present. Canals well 

 developed. 



Under peripheral parts of stom- 

 ach-pouches. 



Entoderm of stomach and ten- 

 tacles citron-yellow or rose-red 



Tropical Pacific. Often near 

 surface. 



M. rhodina Haeckel=jE. 

 canadensis Haeckel. 



Pyriform with high apex. 40 

 to 50 wide, 20 to 30 high. 



4 to 10 in each inter- 

 peronial quadrant. 



A simple, round opening. 



8 with entire uncleft outer 

 edges. Pouches extend less 

 than half the distance from 

 central stomach to bell- 

 margin. 



Present. Canals well-devel- 

 oped. 



Under entire areas of 8 stom- 

 ach-pouches. 



Tentacles red. Stomach and 

 gonads red or green. 



Tropical Atlantic. Often 

 found at or near surface. 



JE. eschscholtzii Haeckel 

 = M. rhodina? 



Rounded. 20 wide, 20 high. 



4 long, triangular lips. 



8 simple, with entire outer 

 edges, as in M. rhodina. 



Present. 



As in M. rhodina. 



Azores, Atlantic. 



♦Species of .■Egina known only from immature specimens are not recorded in this table. Tor 

 For Mgina brunnea and M. alternans see text. 



references to these, see text. 



