156 M. T. Thorell on the Morphology of the Argulidae. 



hazardous such a proceeding is apjjears at once from the fact 

 that, according to Heller's description, the mouth-tube in 

 another American species, A. Nattereri, only contains one pair of 

 chewing-organs, of an entirely different appearance from the cor- 

 responding parts in A. catostomi. That considerable differences 

 exist also between the oral organs of A. foliaceus and A. cato- 

 stomi is apparent at once on a comparison of Dana's and Herrick's 

 description and figures of, for instance, the mandibles and 

 maxillae in the latter species with the account given further 

 on of the same parts in A. foliaceus. According 'to Heller and 

 Cornalia, the genus Gyropeltis agrees with A. Nattereri in having 

 only one pair of jaws in the mouth-tube. In that genus this 

 consists apparently of an upper lip anterior and a lower lip 

 posterior to the jaws; in the Argulidae which have a sting 

 (" gadd") before the mouth-tube, this latter must be formed of 

 the lower lip only, whereas the " sting'' is a transformed upper 

 lip, as indeed Vogt and others have held. 



Of the authors who have described the Argulidae none have ad- 

 vanced further than those already quoted towards a clear exposition 

 of the nature of the mouth; the only species with respect to whose 

 oral organs we possess satisfactory information are consequently 

 Argulus catostomi and Nattereri, together with the three species 

 of the genus Gyropeltis. Even Kroyer, who was the last to occupy 

 himself with these animals, and who gave complete descriptions 

 and figures of several species of them, neglects the struc- 

 ture of the mouth to such an extent that he does not even 

 inform us whether his species possess a sting ("gadd") or not — 

 a point all the more important since, to judge from his figures, 

 they seem to lack that organ whose presence would constitute 

 one of the characters distinguishing Argulus from Gyropeltis. 

 As to the form and number of the footjaws no information what- 

 ever has been vouchsafed. It is, however, evident that a natural 

 arrangement of this rapidly enlarged group, without a know- 

 ledge of the structure of these important oi'gans, must be im- 

 possible or in a high degree difficult to arrive at. 



Of Argulus foliaceus I have been able to have recourse to a 

 few specimens in spirits only ; consequently the following descrip- 

 tion of its oral organs is not so complete as I could have wished. 

 The structure of the sting ("gadd") is given with sufficient 

 accuracy by Vogt and Leydig, and may therefore be passed 

 over here. Its function is probably only that of an irritating 

 organ, whose puncture occasions a strong flow of blood to the 

 spot where the animal is about to suck. 



The mouth-tube has, as is known, a recurved, conical, or 

 club-like appearance ; in a very young specimen I have 

 fancied I perceived signs of a suture of some extent along 



