parasitic on an Ocfo2)us. 475 



Pol'/puff ergasticus from the west coast of Ireland, 600— 

 700 fatlioiiis. 



Tlie occurrence of a parasitic Harpacticid in the unusual 

 situation in wliich this species was found, tliou^h not so 

 strange as is the case of Bahenophilus, deseribed by Auri- 

 villius from the baleen plates of the blue whale, is not without 

 interest, and the two species may well be compared. In both 

 instances we have isolated species belonging to, or closely 

 allied to, non-parasitic families, specially modi tied for an unusual 

 manner of life. In Cholidi/a the moditication has gone much 

 further than in Balfpno/Ju'hcs^ and, had not the first ))air of 

 feet remained unmodified, the relationship to I(I>/a might 

 liave been overlooked, as most of the other appendages, taken 

 separately, are common to other groups, bi>th para-sitic and 

 free-living. \\\ Baleen ophilus, on tlie other hand, the ad;\{)ta- 

 tions to its peculiar mode of life are so slight that its relation- 

 ship to Harpucticus is at once apparent, and it would be 

 difficult to make sure that it had a parasitic habit were it3 

 place of origin unknown. The genus /(/c/c/, by the possession 

 of strongly chelate maxillaj and maxillipedes, seems well 

 adapted to give rise to a parasitic race, as the means of 

 attachment are already present. 



These instances of parasitic forms — as it were, in the 

 making — throw some liglit on the origin of the various families 

 of parasitic (^j]>epoda in general, many of which, it is probal)le, 

 have started iiKlependenlly as modifications of widely separated 

 non-parasitic species. 



EXPLANATIUN OF PLATE XXf. 



ClioUilya polypi, $ . Ventral view. 



„ ,, First unteiiiia. 



„ „ Second antenna. 



„ ,, Mandiljlt". 



„ „ Ywat maxilla. 



„ „ Second lua.xilla. 



„ ,, Maxilliijede. 



,, „ First foot. 



,, ,, Second Coot. 



„ ,, Fifth fout. 



„ „ Genital openings. 



,, „ Furca. 



