270 M.T.Thorell on the Systematic Position of the Argulide. 
Argulide than to any other group of the Crustacea. Even 
Vogt expresses himself against the union of the Argulide with 
the Siphonostoma, on the ground that the organization of the 
mouth is very different ; but he says nothing further as to their 
place in the system. 
The order Branchiopoda only can claim a stronger affinity 
to the Argulide on the ground of several leading points of 
resemblance. The relation of these latter to that order had 
already attracted the notice of authors who ranged them with 
the Siphonostoma, as, for instance, Milne- Bdwands. who says, 
with reference to the swimming- ee of the Argulide, that they 
seem to be intermediate between those of the Branchiopoda and 
of the ordinary Siphonostoma. Zenker is, however, the first 
who made a decided step in this direction, and in his Crustacean 
system united them with the Branchiopoda, at the same time 
drawing attention to their marked agreement with these in cer- 
tain important points, as the structure of the eyes and digestive 
apparatus, and showing also that the greater number of the 
characters which were “thought to justify their amalgamation 
with the Copepoda are also to be found in many Branchiopoda. 
This notion of Zenker as to the systematic position of the Argu- 
lide has been shared by Gegenbaur and myself*, as also by 
Steenstrup and Luetken, who ally Argulus to the Phyllopoda, 
as the representative of parasitism in that group. 
A renewed examination of the structure of the Argulide, as 
compared with that of the Copepoda and the Branchiopoda, has 
further convinced me of the correctness of Zenker’s view. I 
have fancied that I could discover grounds for making the Ar- 
gulide a suborder of the Branchiopoda, consequently a group of 
equal value with the Phyllopoda and Cladocera, although most 
nearly allied to the former; and as I shall now proceed to an 
exposition of those grounds, I have only to hope that such may 
in some measure contribute to the final solution of the question. 
Such an examination has appeared to me all the more necessary 
since Kréyer has lately become a champion of the old view of 
the position of the Argulide, and has sought to prove their 
affinity with the Copepoda by several considerations which lave 
been more or less overlooked by previous authors, who founded 
their ideas of the propriety of mserting the Argulide among 
the parasitic Copepoda exclusively on the suctorial formation of 
the mouth and the parasitic habits depending thereon. 
In order to form a clear notion of the relations of the Argu- 
lide to the Copepoda and Branchiopoda, it is necessary to 
determine the reciprocal relations of these two groups; 7. e. to 
* « Bidrag till kannedomen om Krustaceer, som lefva i arter af slagtet 
Ascidia, L.,” K. Vetensk.-Ak. Handl. Bd. ii. No. 8 (1859-1860), p. 14. 
