432 Dr. F. Miiller-on Philomedusa Vogtii. 
LVI.—On Philomedusa Vogtii, a parasite on Medusa. 
By Fritz Mixer, of Santa Catharina*, 
[With a Plate. ] 
Tue Meduse are infested by the most various parasites. Infu- 
soria swim about in the testes of Tamoya; Trematoda and other 
Entozoa often occur in abundance in the gelatinous substance 
of different species; Isopoda, Amphipoda, and a Palemon of 
glassy transparency, move about in the mucus of the disk and 
arms, the urticating filaments of which cause rapid death to 
other Crustaceans; and a Crab (Libinia?), of gigantic size 
compared with its host, is in the habit of taking up its 
abode between the four columns bearing the arm-plates of the 
Rhizostomide. But it appeared to me that the most remarkable 
of all these parasites, and one well worthy of a particular de- 
scription, is the Helianthoid Polype to which the following pages 
are devoted, partly as it is the first parasitic species of its group, 
and partly because its almost Acalephoid transparency enables 
us to make an easy and certain inspection of its certainly very 
simple anatomical conditions. 
Philomedusa Vogtii, which is the name I give to the animal, 
appears, when it has dilated the cavity of the body with water, 
in the form of a cylindrical sac, of about 30 millim. (rarely over 
50 millim.) in length, and 5 millim. in thickness. The posterior 
extremity is usually slightly diminished, rounded-off in a sphe- 
rical form, or more or less drawn in like a funnel. At the an- 
terior extremity there is a circle of twelve short (about 4 millim. 
in length), thick, cylindrical tentacles with rounded, closed 
apices, which are sometimes carried expanded in the same plane, 
sometimes extended obliquely forwards, but most frequently bent 
back towards the posterior extremity. All the tentacles are 
nearly of the same length; nevertheless we may distinguish six 
longer ones, and six shorter ones alternating with these, although 
this inequality is frequently effaced by their different states of 
contraction. Commencing between each pair of tentacles, twelve 
shallow longitudinal furrows traverse the surface of the body, 
and meet together in a radiate form in the middle of the poste- 
rior extremity. The colour of the animal in this state is limited — 
to a whitish turbidity; when the animal is most strongly con- 
tracted, which usually gives it the form of a fig with twelve 
longitudinal furrows and numerous transverse wrinkles, the co- 
lour is concentrated to a dingy yellow, with more or less of a 
reddish tinge. The tentacles sometimes appear of a slightly 
reddish colour; and at the base, on the inside, there is usually 
* Translated from Wiegmann’s Archiv, 1860, p. 57, by W. S. Dallas, 
F.L.S. 
