432 Dr. F. Miiller on Philomedusa Vogtii. 



LVI. — On Philomedusa Vogtii, a parasite on Medusa. 

 By Fritz Muller, of Santa Catharina*. 



[With a Plate.] 



The Medusae 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 Palamion 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 

 Rhizostomidse. 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. 



