M. T. Thorell on the Morphology of the Argulide. 153 
blish another view respecting them, tending principally, as it 
would seem, to discover a nearer affinity between the Argulide 
and the Caligide, in which latter group, as in the parasitic Crus- 
taceans in general, it is not the first but the second pair of an- 
tenn which take the form of fixing-organs. According to 
Kroyer, that which I have called the first pair of antenne con- 
sists of both pairs of antennz coalesced ; the appendage would 
thus be the first, the claw itself the second pair of antenne. In 
accordance with this view, the real second pair of antenne is re- 
garded as the first pair of footjaws. After what has been already 
said relative to the history of the development of these organs, a 
detailed refutation of Kroéyer’s hypothesis would be superfluous. 
With regard to the other appendages of the head, a comparison 
between them in the Argulidee and the groups allied thereto is 
rendered difficult by the circumstance that the Argulus-larva at 
its exit from the egg is much more fully developed, and already 
furnished with the parts belonging to the mouth, and also with 
the two pairs of limbs situated behind these, so that the origins 
of these parts cannot be followed genetically. One may, how- 
ever, conclude from analogy that in the Argulus, as in the Phyl- 
lopods and Copepods, the mandibles are formed out of the base 
of the second pair of feet in the larva, and the maxille behind 
them as an independent pair of limbs. How far the two following 
pairs of limbs in the-Argulide are originally, as Claus* showed 
to be the case in the free Gnathostoma and in at least a part of 
the parasitic Copepoda, branches of one and thé same pair of 
limbs is certainly not clearly ascertained: nevertheless their 
form and position (especially in the larvee) exhibit too evident 
marks of correspondence with the footjaws in the higher families 
of Siphonostoma to admit of their being regarded in their origin 
and morphological significance as bearing no relation to these. 
The first pair seems to serve exclusively as fixing-organs: they 
take, as is known, in the adult state of the different species of the 
genus Argulus the form of sucking-cups, while in the larvae 
and in the genus Gyropeltis they are armed at the extremity with 
a hook. The functions of the second pair are not equally easy 
to determine; but if they serve to maintain the animal when 
fastened on its prey, they probably also, and perhaps principally, 
serve as organs of locomotion, and may therefore be called 
“creeping-feet ” (pedes gressorii), as they have, indeed, been 
named by Kroyer. Vogt} maintains that the animal avails 
* Die frei lebenden Copepoden, p. 28 (1863). “ Ueber den Bau und die 
Entwicklung von Achtheres percarum,”’ Zeitschrift fiir wiss. Zool., Bd. ix. 
(1861) p. 293. 
T “Beitrage zur Naturgeschichte der Schweizerischen Crustaceen,”’ Neue 
Denkschriften der allg. Schweizerischen Gesellschaft fiir die gesammten 
Naturwissenschaften, Bd. vii. (1849), p. 12. 
