364 Mr. J. W. Fewkes .on a new 



of another Medusa, Geryonia. We undoubtedly have In this 

 case a modification of the parasite by its peculiar mode of 

 life in the host, although a reciprocal effect on the host is not 

 recognizable. 



Less known than Cunina, although quite as interesting, is 

 the case of Mnestra parasita, a Hydromedusa which lives 

 parasitic on the pelagic mollusk PhylUrhoe. We find here a 

 modification in the structure of Mnestra by the attachment, 

 although we know but little of the nature of tliat modification, 

 while of the growth of the Medusa we know nothing. 



A most interesting instance of parasitism and consequent 

 modification among Medusaj is found in the problematical 

 organism Polypodiuni. This undoubted hydroid is found 

 parasitic in the ova of the sturgeon wliile in the body of the 

 fish. We have in Polypodiuni^ as described by Ussow, a 

 hydroid-like animal, which develops and drops buds which 

 can be directly compared with Medusse. These are not the 

 only instances of parasitic Medusae thus far recorded, but 

 they are typical and useful for comparisons. None of them 

 are as valuable as they might be in estimating the amount of 

 change in anatomy which has resulted, since we are either 

 ignorant of their whole life-history or of that of related adults 

 with simple development. 



It is with the greatest pleasure that I am able to add to the 

 above-mentioned instances of parasitism among Medusae 

 another of most extraordinary character. This instance is 

 peculiarly adapted for the study of the effect of parasitism in 

 modifying the Medusan structure, as its close allies are well 

 known and comparisons with them can be easily made. 

 This instance is, I believe, unique and the first recorded 

 example of a Hydroid living attached to the outside of a 

 fish and modified in structure by its life. It may thus 

 properly be called a new mode of life among Medusae. 



In the pelagic fishing which has been carried on for the 

 last ten years at the Newport Marine Laboratory we have 

 taken several specimens of the well-known fish Scriola zonata, 

 Cuv. This fish is a close ally of the ordinary " pilot-fish," 

 and is often seen in calm weather swimming near the surface 

 of the sea. Three of these fishes were found in company 

 last summer, and upon the side, near the anal fin, of one of 

 these, curious appendages Avere noticed which had never been 

 observed before. On capturing the fish and making a super- 

 ficial examination of the attachment I was reminded of an 

 attached fungus growth. Every one is familiar with the 

 growth on fishes of the fungus Saprolegm'a, and the resem- 

 blance seemed so great, except in colour, between the supposed 



