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Argulus foliaceus. A Contribution to the Life History. 



By Frederick Noad Clark. Read October (^t/i, 1902. 



Classification^ Literature, and Introduction. 



The subject of my paper this evening is Argulus foliaceus, of the 

 class Crustacea, sub-class Entomostraca, family Argulid^, genus 

 Argulus. Biologically, it is more nearly related to theCopepoda than to 

 any other family of the Entomostraca. So far as my information goes, 

 foliaceus is the only species known in Great Britain, although others 

 such as A. coregoni occur on the Continent, and A. catostomi in 

 America. Furthermore one genus only is known. Little has been 

 written in England concerning this interesting creature since Baird's 

 account in his "Natural History of the British Entomostraca," pub- 

 lished by the Ray Society in 1850. Short notes are given by Murray 

 in his "Economic Entomology," and in Cuvier's "Animal Kingdom," 

 vol. iii. Amongst other authorities may be mentioned Dana and 

 Herrick, 1837 ; Gerstiicker, Jurine, 1806; Leydig, and Thorell. By 

 far the best description is that of Professor C. Claus (Vienna), pub- 

 lished in the "Zeitschrift fiir wissenschaftliche Zoologie," vol. xxv, 

 1875, in which he gives an exhaustive account of the development 

 and organisation o^ A. foliaceus. 



Commonly called the "fish louse," Argulus is found parasitic on 

 various fresh-water fish, e. g. carp, roach, tench, stickleback, etc. It 

 is from the Gasterosteus aciileatus, or three-spined stickleback, I 

 have obtained my specimens. It is recorded to have been found on 

 frog and toad larvae, and on the minnow, but seldom on pike, perch, 

 or salmon-trout. My observations commenced in 1896, since when 

 I have had good opportunities of studying its life history, having 

 repeatedly bred them from the egg to the adult stage, and so on 

 again. By reason of its exceptional structural character, the elaborate 

 nature of its apparatus for attachment to its host, the interesting 

 details of its metamorphosis, and the curious organs and mode of 

 reproduction, I venture to say that a study of the Argulid^e will well 

 repay the scientific observer. 



I will refer later on to a more detailed description of the anatomy 

 of this creature, and for the present will describe it briefly as a trans- 

 parent, jelly-like animal of a greenish hue, the bulk of whose body 

 appears as a slightly convex carapace, which entirely covers the ■ 

 various organs with the exception of the eyes, swimming-feet, and 

 tail (so called). The adult female measures 8 mm. long by 6 mm. 

 broad. The male is slightly smaller, and may be distinguished from 



