LIMULUS AN ARACHNID, 633 
blance to the central and lateral eyes of Limulus, the 
Kurypterina, and the Scorpions. 
When we examine the appendages, one striking resem- 
blance is seen between the males of some free-living Cope- 
pods, on the one hand, and Limulus and Pterygotus, on the 
other. The first pair of appendages is in these forms pre- 
hensile. No other Arthropods except Arachnida have 
such a form of the first appendage. But many Eurypterina 
have non-chelate anterior appendages (see fig. 20), and the 
comparison of appendages in various Crustacea shows clearly 
that such a modification is readily acquired and readily sup- 
pressed. In one other respect some appendages of some 
Copepoda appear to resemble those of Limulus, viz. in the 
union of the basal portions of the swimming feet. In 
Limulus, however, this union is effected rather by the 
upgrowth of a median sternal process than by the coales- 
cence of the bases of the appendages themselves. 
In other respects the appendages of Copepoda are quite 
unlike those of Limulus and the Eurypterina in form, and 
they do not agree with them in number. Those near the 
mouth have jaw-like coxz, as in all Crustacea, but they, have 
the usual Crustacean elements of endopodite, exopodite and 
epipodite more or less clearly developed, and are not simple 
rami, as are those of the Eurypterina. What may have been 
precisely the character of the limbs on the segments following 
the carapace in Eurypterina we do not know, but there is 
reason to suppose them to have been lamelligerous, and that is 
their distinguishing feature in Limulus. No such lamel- 
ligerous appendages are known in Copepoda, but in the region 
which might be compared to that carrying the genital 
operculum and the five lamelligerous appendages of Limulus 
—were it not for the fatal difference indicated by the reversed 
position of the generative orifices—we find four or five pairs 
of simple biramose swimming feet. 
In internal organisation there is nothing in the characters 
of the nervous, digestive, reproductive, or circulatory organs 
(such as are present) of the Copepoda to suggest an alliance 
with Limulus, whilst the presence in the former of the 
characteristic Entomostracous shell-gland marks a special 
divergence between them. It is true that Packard has 
assimilated a brick-red coloured structure occurring at the 
base of the cephalothoracic limbs of Limulus to a shell- 
gland, or to a renal organ. In this I cannot agree with 
him. It is not even apparent, at present, that this brick- 
red organ, which I have examiued, is of a glandular nature 
at all, 
