3IO DISCOVERY REPORTS 



Apart from the number of radial canals and lobes to the stomach there is nothing 

 to indicate that the specimens with eight main radial canals are specifically different 

 from the six-rayed specimens, and the occurrence of several with five, seven, nine, 

 ten or eleven main canals further confirms the supposition that the examples of 

 Willia at the Falkland Islands all belong to one species, the most characteristic 

 feature of which is its extreme variability. The six-rayed specimens are so much 

 like W. stellata that they might be considered to belong to that species. In W. stellata, 

 however, six is the absolutely dominating number of rays, and specimens with other 

 numbers are altogether irregular in shape ; eight main radial canals regularly arranged 

 are never seen in this species, whereas it is the number most commonly found in the 

 Falkland medusa. It seems reasonable, therefore, at least provisionally, to regard 

 W. mutabilis as a proper species. There also seems to exist some difference in the mode 

 of branching of the radial canals. In W. stellata the two first lateral branches are 

 opposite each other, issuing on either side of the main canal and fairly close together. 

 In W. mutabilis, regardless of the number of main canals, the two first branches come off 

 rather far from each other and frequently both on the same side of the main canal, or 

 the second branch comes off from the first one and not from the main canal itself. 

 W. stellata occurs in northern Europe and in Japan. Another Japanese species, 

 W. pacifica Maas, has likewise six main radial canals ; it is distinguished from stellata 

 by the much greater number of terminal branches and tentacles ; Uchida (1930, p. 334) 

 considers it a proper species. A very interesting species is W. brooksi Mayer (1910, 

 p. 194) from Beaufort, N.C., in North America; it has six main radial canals, but the 

 stomach is not divided into six equal lobes but forms three lobes each of which is 

 bifurcated, in the same manner as the four primary lobes in young specimens of 

 W. mutabilis with eight main canals as described above. This species further demon- 

 strates the variability in the conformation of the medusae within this genus. 



The genus Proboscidactyla is characterized by the number of main radial canals and 

 lobes to the stomach being four and not six or more as in Willia. As demonstrated above, 

 however, when eight main canals are found in W. mtitabilis they are not of equal origin, 

 and the fundamental number is really four, as in Proboscidactyla. If in a Proboscidactyla 

 the four stomachal lobes, with the gonads, were to proceed with their outward growth 

 beyond the first division of the main radial canals, the medusa would attain an appear- 

 ance very like that of the intermediate stages of Willia mutabilis with eight main canals. 

 Such prolongation of the stomachal lobes has actually been observed in specimens of 

 Proboscidactyla oriiata var. stolonifera from the west coast of Mexico (Bigelow, 1909, 

 p. 220, pi. 41, figs. 1-7) and in P. variatis Browne from India. Accordingly, the limit 

 between the two genera Willia and Proboscidactyla is not so sharp as formerly supposed. 



Menon (1932, p. 13) has described a medusa from Madras in India which he called 

 Proboscidactyla conica. The stomach is cross-shaped in transverse section and has 

 several radial lobes; there are several branched radial canals and thirty-five to forty- 

 five tentacles. The specimen figured (pi. ii, figs. 12-13) bears a striking resemblance 

 to irregular specimens of Willia mutabilis. 



