33 



II.— LEEN^A. 



The Lern.eice, although not so extensive a family in 

 numbers of genera and species as the Caligid.e, are more 

 interesting to the specialist. They present some of the 

 most remarkable instances of retrograde development that 

 are to be found in the whole group of parasitic Copepoda. 

 There is great excuse for the difficulty experienced by the 

 earlier Zoologists in giving certain members of this family 

 their true place in the animal kingdom. The fact that 

 these animals were placed first in one grouj) and then in 

 another by successive workers is not surprising, consider- 

 ing- that nothing was then known about their life history. 

 It requires some study even at the present day to show 

 that Lerncea is a Crustacean, still more to demonstrate 

 that it is related to Lepenphtheirus. 



The genus Lerncea as it now stands contains only five 

 species. Formerly it was ver^^ extensive, and included 

 many forms, such as Lepeophtheirus j^^f^toi'alis, that had 

 not the least apparent resemblance to each other in the 

 adult state. Careful research, along with a better know- 

 ledge of the minute striicture, gradually eliminated the 

 unlike species, which were removed to other genera. An 

 excellent historical account of our knowledge of the group 

 will be found in Baird's " Entomostraca." 



The species described here is Lernaa branchialis, Linn. 



Mode of Occurrence. 



The adult female is found on the gills of the Gadidse, 

 such as cod, haddock and whiting. Immature (cyclops 

 stage) males, and females with adult males attached, are 

 found on the apex of the gill filaments of the flounder, 

 sometimes in large numbers. Full-grown females are 

 not plentiful on the fishes caught in the vicinity of Piel. 



