6 M, F* Miiller on the Systematic Position of the Charybdeidse. 



Fig. 5. Cypris Verreauxii, on its side, magnified 20 diameters ; 5 a, the 

 same, seen from underneath, magnified 20 diameters. 



Fig. 6. Cypris Yallahensis, on its side, magnified 40 diameters ; 6 a, the 

 same, seen from underneath, magnified 40 diameters, with natural 

 size annexed. 



II. — On the Systematic Position of the Charybdeidse. 

 By Fritz Mltller*. 



Eschscholtz's section of the Discophorce phanerocarpce formed 

 a well-defined group of closely allied animals, united by a great 

 number of common characters : — the disk a shallow and smooth 

 segment of a sphere, but capable of being more strongly arched 

 during natation, with a notched margin, in the notches of which, 

 always to the number of eight, are the marginal corpuscles with 

 crystals insoluble in acids; round the mouth four arms, and 

 alternating with these, in peculiar pits, the sexual organs, form- 

 ing bowed bands folded like frills ; the stomachal filaments in 

 the same place, and so forth. The mouth, indeed, was sometimes 

 freely open (Medusida) and sometimes closed, and, instead of it, 

 numerous orifices on the arms (Rhizostomidce) ; but this pecu- 

 liarity of the Rhizostomidce, important as it certainly is for their 

 mode of obtaining nourishment, did not disturb the morpho- 

 logical unity of the group, as it is derived without difficulty from 

 the ordinary form of mouth f. Some subsequently discovered 

 somewhat anomalous forms of Medusidce likewise did not pre- 

 judice the unity of the general picture, which they only served 

 to complete J. 



* Translated from Wiegmann's 'Archiv,' 1861, by W. S. Dallas, F.L.S. 



t Gegenbaur (Zeitschr. fur wiss. Zool. viii. p. 210, note) declares the 

 polystomism of the Rhizostomidce to he a paradox not reconcilable with 

 the general plan of the Medusce, and even doubts the fact. The fact is 

 easily ascertained, and has lately been repeatedly proved, even by myself. 

 Its explanation also seems to me to be pretty easy. A temporary poly- 

 stomism, if it may be so called, may be easily seen in Hydroid Medusae, 

 where the margins of a much-folded four-lobed oral fringe lie upon each 

 other here and there. Thus also the polystomism of the Rhizostomidce will 

 result from the growing together of the membranous laminae which sur- 

 round the arms of the Phanerocarpce. When the orifices of the arms 

 have the form of long slits, often continued into strap-like tentacles, as in 

 a Cephea of the South-Brazilian coast, scarcely any doubt can remain as 

 to this mode of production. It seems more difficult to explain the perfora- 

 tion of the peduncle of the arms, or its " origin with four roots," as occurs 

 in the same Cephea, and, accordiug to Forskal, in C. octostyla. 



X Such as Nausithoe, K611., with its eight extremely simple sexual glands, 

 and Trichoplea, n. g., with marginal corpuscles in deep niches on the under 

 surface, two inches from the undivided margin of the disk, which measures 

 two spans in diameter. Amongst the older, less accurately-known species, 

 Medusa persea, Forsk. (Rhizostoma, Eschsch.), is certainly to be placed with 

 the " Acraspeda," notwithstanding its undivided margin and large velum. 



