282 M.T. Thorell on the Systematic Position of the Argulide. 
gland” in Argulus opens through the “ sting,’ which has not 
yet been attested from observation, then it is only the spine 
Just mentioned on the second pair of antenne in the Caligide 
and Cytheridz (consequently in animals belonging to two dif- 
ferent orders) which can be compared with the sting in Argulus. 
As the “ poison-gland ” itself occurs in many widely separated 
orders, it is easy to see that its presence in the Argulide in no 
way points out their zoological affinity; and should it open 
through a spine in some parasitic Copepoda, these would be in 
the same relation to Cyclops and Cyclopsine (which lack such an 
organ) as that which the parasitic Argulus with sting bears to 
the free Branchiopoda without sting. 
Kroyer produces two further reasons for his view of the sys- 
tematic position of the Argulide, which it now remains for us 
to remove. The first is “the absence in Argulide of external 
egg-sacs—which finds its analogy in the genera Notodelphys, 
Doropygus, &c.” It seems to us, on the contrary, quite obvious 
that the absence of external egg-sacs goes to prove that the 
‘ Argulidz are not Copepods, since these, with the exception of 
the Notodelphyidee and Buprorus, generally have external egg- 
sacs, as 1s also the case in particular with the Caligide and all 
the other Siphonostoma with which the Argulid would be ranged 
were they Copepods. The asserted analogy is, moreover, very 
feeble; for in the Argulide the eggs stand on the ovary itself 
until they attain freedom, whereas in Notodelphys &c. they 
pass from the ovaries into a matrix comparable with the 
so-called uterus in the Branchiopoda, or, still better, with the 
matrix of the Cladocera. 
Kroyer finds the last attestation of the Copepod nature of the 
Argulide in ‘the simple eyes placed in a triangular form, which 
recur not only in the free-swimming Copepods (Sapphirina), 
but also in the parasites in the larval state.” With reference to 
this, we have only to remark that an unpaired eye, retained after 
the larval period, without or with two, three, or several crystal- 
line bodies (“simple eyes’’), is quite usual, not only among the 
Copepoda (where it generally constitutes the sole visual organ), 
but also among Phyllopoda, Cladocera, and other lower Crusta- 
ceans, and that consequently the presence of such an eye in 
Argulus in no way proves its relationship to the Copepoda. 
Further, Kréyer’s representation of the structure of this single 
eye in Argulus is incorrect ; for what he calls three simple eyes 
are in that animal a three-lobed prolongation of the brain itself, 
bearing a pigment-spot, in which not a trace of erystalline bodies 
or “simple eyes” is to be detected, at least in either A. folia- 
ceus or A. coregoni. The unpaired eye in many Branchiopoda 
(as Branchipus and Artemia) also shows itself as such a pigment- 
