10 Mr. P. W. Bassett- Smith on 



of Chondracanthus zei, which, from its large size, would seem 

 to be at least inconvenient to its host. 



The gills of the turbot and brill are frequently crammed 

 with. Lepeophtheirus Thompsom und Lepeophtheirus obscurus (?) 

 and so on, each fish liaving apparently in its adult stage one 

 or more parasitic Copepoda. 



Ai'ter the examination of a great number of fish harbouring 

 these parasites I believe that in the great majority of cases 

 their presence is not prejudicial to the life of the fish, seem- 

 ingly causing neither irritation nor destruction of tissue, for 

 the following reasons : — 



(1) The fish bearing them were generally mature. 



(2) There were rarely any ulcerated surfaces found 



around or near their attachment. 



(3) The individual fish were generally well nourished. 



There are, however, certain exceptions to this absence of 

 prejudicial effect on the host. 



(1) Lernea hranchialis and its allies, whose bodies are full 

 of sanguineous fluid. The head and cephalic processes, 

 d^ply imbedded in a cysted clot of blood in and around the 

 gills, must be a constant source of drain of nourishment and 

 also cause great irritation to the hosts. Very frequently, 

 however, one came across the remains of their chitinous necks 

 still imbedded, from which the bodies had fallen away. 



(2) A second, which certainly causes much irritation to the 

 fish, is Cliondracanthus merluccu, which, though surrounded 

 by mucus and probably living on mucus, causes great 

 destruction of the membrane where it is attached, as already 

 mentioned. The other species of Chondracanthus apparently 

 are not so troublesome, so far as I have seen. 



(3) All species of Lernaocera^ Lernceonema, and Penella 

 must be harmful. 



I do not, however, mean to infer that weakly and diseased 

 fish are not more likely to suffer from these parasites, but that 

 they are plentiful in those apparently healthy. 



The curious attached condition of the young of the Caligidse 

 has been much noticed, being by Burmeister, Milne-Edwards, 

 Kroyer, and Baird regarded as a separate genus, Chalimus ; 

 but their true nature is very well shown in the able mono- 

 graph by Hesse, ' Des moyen curieux de certains Crustaces 

 parasites ' (Paris, 1866) , though I do not think his theory, 

 " that the males in the interest of propagation fix themselves 

 by this singular means (the frontal filament) to the females," 

 is of much value, as these attached forms are not infrequently 



