On the Structure and Affinities of Mnestra parasites Krohn etc. 47 



Greographical Distribution. 



Mnestra parasites lias been recorded from Messina and tlie Bay 

 of Naples. PJujlUrho'é is an alraost world-wide genus; its several 

 species bave been foimd to inhabit tbe N. and S. Pacific, the Indian 

 Oceau and S. Atlantic as well as the Seas of Southern Europe. Yet 

 if a sessile medusa infested such a large proportion of the exotic as 

 of the Mediterranean individuals, it could hardly bave escaped the 

 notiee of such accurate describers of PhylUrhoe as Quoy & Gaimard, 

 Eydoux & SouLEYET, or Macdonald. We are tberefore justified in 

 statìng that the evidence is in favour of Mnestra jiciras^ites being 

 confined to the Mediterranean and possibly adjoining seas. 



The relation of the Mnestra to the Phyllirhoe. 



Is tbe relation between Mnestra and Phyllirhoe one of parasitism 

 or one of symbiosis? 



Ali through tbe present paper, tbe opprobrious epitbet "parasitic" 

 bas been avoided and tbe less inferible "sessile" has been employed. 

 There is no doubt but that tbe adult Mnestra like a vampire lives 

 by bloodsucking and there also seems reasou to believe that its young 

 may be parasitic ab ovo; but may not the Phyllirhoe derive some 

 advantage from tbe Mnestra it bears? 



Tbe facts pertiuent to the present discussion seem to be 



1. That more than half of tbe Phyllirhoe examined were in- 

 fested by Mnestra. 



2. That tbe Phyllirhoe does not seem to be appreciably bandi- 

 capped in its swimming powers by its bürden. 



3. That tbe Mnestra was never found attached to any part of 

 a Phyllirhoe except to tbe "tbroat", upon tbe ventral margin 

 of the body immediately beneatb the junction of tbe Oeso- 

 phagus wìth the stomach. 



4. That tbe exumbrella of the Mnestra is well equipped with 

 nematocysts whicb on account of their position are useless 

 for attack against the Phyllirhoe, but whicb bave been observed 

 to bave been used witb effect against another animai. 



