M. T. Thorell on the Morphology of the Argulidse. 155 



ingArgulus foliaceuSfSind even the distinguished Jurine*, assumed 

 that the oral aperture was situated at the tip of the anteriorly 

 produced sting (" gadd," aculeus or stimulus) in that animal, 

 and consequently missed all acquaintance with the essential 

 parts of the mouth. For the first exact description of these 

 parts in an Argulid we have to thank Dana and Herrick, who, 

 in their admirable memoir already cited, on Argulus catostomi, 

 have given an accurate representation of the structure of the 

 mouth-tube in that American species, and have shown that it 

 contains two pairs of organs. These they designate inner and 

 outer maxilla ; the sheath itself which contains these they regard 

 as corresponding to the mandibles, — a view which is in accordance 

 with these authors' attempt to show a like segmentation and 

 number of the appendages in the Argulidse to those which obtain 

 in the Decapoda — consequently, as in those, one pair of mandibles 

 and two pairs of maxillse. 



Several years later Vogt gave a description of A. foliaceus, in 

 which Jurine's mistake as to the position of the mouth is recti- 

 fied; but the exposition which Vogt puts forth of the oral 

 organs is far from clear, as is the case also with the figure which 

 accompanies it. The following is Vogt's description : — " The 

 opening of the mouth is situated in a club-shaped pi'ojection 

 behind the * sting,' protected on each side by two ring-like 

 horny plates inclined inwards; and on the inner surface of 

 these are seen two smaller plates of similar appearance. A sin- 

 gular S-shaped double lip is seen below, which is inclined up- 

 wards, and opposed to a single horny piece bent over the open- 

 ing above." 



Leydig, who has written an excellent memoir on the inner 

 conformation of A. foliaceus, has also briefly named the oral 

 organs and described them as follows : — " The opening of the 

 mouth is placed in a club-shaped projection bent downwards. 

 It is bounded posteriorly by a crescent-shaped lower lip, an- 

 teriorly and laterally by two broad gradually tapering plates. 

 Several disk-like pieces inside represent the mandibles." 



It will be seen that this description also is not satisfactory, 

 since it gives no further light on the form and number of those 

 parts which are said to correspond with the mandibles. These 

 two authors, Vogt and Leydig, would seem to be the only ones 

 who have given any exposition of the armature of the mouth in 

 A. foliaceus based on independent researches. Others, as 

 Milne-Edwards and Bairdf, have, further, applied to the Euro- 

 pean species Dana's and Herrick's representation of the struc- 

 ture of the oral organs in the American A. catostomi ; but how 



* Loc. cit. p. 440. 



t Nat. Hist, of Brit. Entomostraca (1850), p. 248. 



