156 M.T.Thorell on the Morphology of the Argulide. 
hazardous such a proceeding is appears at once from the fact 
that, according to Heller’s des¢ription, the mouth-tube in 
another American species, 4. 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- 
stomt is apparent at once on a comparison of Dana’s and Herrick’s 
description and figures of, for instance, the mandibles and 
maxille im 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 Argulide 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 Argulidz 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 organs, must be im- 
possible cr 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 
