152 M.T. Thorell on the Morphology of the Argulide. 
differently regarded, this is certainly the case in a like or even 
greater degree with the accessory organs, especially the anterior 
ones or those which appertain to the head. We shall treat of 
those which belong essentially to the mouth further on, and 
would begin by directing our attention especially to the four 
pairs of members which are situated before and behind these. 
The views taken of these organs, of which we call the two fore- 
most pairs the first and second pairs of antenne, and the two 
hindmost the first and second pairs of footjaws, have, as we have 
said, been very various, doubtless through erroneous notions of a 
complete correspondence between the accessory organs of the head 
in the lower Crustaceans and in the Decapoda, which has rendered 
the terminology of the former so confused and contradictory*. 
Of the antenne one pair has usually been considered a pair of 
footjaws,—the first pair by Heller and Cornalia, the second by 
M.-Edwards and Kroyer. The view we have taken agrees with 
that given by Dana and Herrick}; and its correctness 1s shown, 
not only by the form and position of the corresponding parts in 
the Phyllopods and Copepods, to which the Argulidz are most 
nearly allied, but also by the history of their development. The 
newly hatched larva of Argulus has, as Jurine’s{ and also 
Dana’s and Herrick’s figures attest, a pair of antenne and two 
pairs of swimming-feet, like the larve of the Phyllopods and 
Copepods; and since the organs which are deveioped from the 
antennz and first pair of jaws in the Phyllopod and Copepod larvze 
are now generally regarded as the first and second pair of antenne, 
the same rule should be applied to the Arguhde. <A glance at 
the larva of an Argulus shows immediately that the conditions are 
here just the same as in the case of the Phyllopod and Copepod 
groups; the sole difference between the Argulide and these is 
that the antennz in the Argulus-larva gradually attain a hooked 
form, becoming hooked fixing-organs through a stronger deve- 
lopment of their two first joints, while the other joints are corre- 
spondingly reduced and at last form only a small appendage to 
the second joint of the antenne. The first pair of feet im the 
larva is, as is usual in the allied Crustacea, biramose ; the hinder 
branch already exhibits the form of the adult animal’s second 
pair of antenne ; the foremost branch disappears during the de- 
velopment of the larva. 
I should not have dwelt so long on the antenne of the Argu- 
lide were it not that Kroyer§ has very lately sought to esta- 
* Vide Claus, “‘ Zur Morphologie der Copepoden,”? Wiirzburger Natur- 
wissenschaftliche Zeitschrift, Bd. 1. (1860) p. 26 &e. 
+ Deser. of Arg. catostomi, Silliman’s Journal, vol. xxxi. (1837) p. 298 &e. 
{ Mémoire sur l’Argule foliacé, Ann. du Mus. t. vii. (1806) pl. 26. fig 4. 
§ Loe. cit. p. 87. 
