M. T. Thorell on the Morphology of the Argulide. 155 
ing Argulus foliaceus, and even the distinguished Jurine*, assumed 
that the oral aperture was situated at the tip of the anteriorly 
produced sting (“ gadd,” aculeus or stimulus) m 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 catostomt, 
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 maxille ; 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 Argulide to those which obtain 
in the Decapoda—consequently, as in those, one pair of mandibles 
and two pairs of maxillee. 
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 projection 
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 Baird+, 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 
* Loe. cit. p. 440. 
+ Nat. Hist. of Brit. Entomostraca (1850), p. 248. 
