626 PROFESSOR E, RAY LANKESTER. 
and exhibit a considerable range of character, being (as in 
other Arachnida) either ambulatory or tactile organs. The 
chelate limbs are thus seen to be a special feature of Limu- 
lus, and not essentially characteristic of the Limuloid Arach- 
nida. Accordingly there is no difficulty in deriving the 
Scorpion’s ambulatory limbs from those of such Limuloids. 
Thirdly, certain features are presented by the cephalo- 
thorax of the Eurypterina, in which they agree very closely 
with the Scorpions, and in which Limulus differs from them. 
A great difference between Limulus and Scorpio, leading 
to differences in the form and size of internal organs, is that 
presented by the much greater size of the cephalothorax in 
Limulus. Among the Eurypterine Limuloids we find, how- 
ever, genera, in which the cephalothoracic carapace has 
precisely the quadrangular shape and small relative size, as 
compared with the abdomen, which is noticed in Scorpion 
(fig. 20). It cannot be doubted that the packing of the 
viscera was correspondingly affected, and there is great pro- 
bability that the liver was connected by more numerous 
ducts with the intestine in these forms (as in Scorpion) 
than it is in Limulus. It is also probable in the very 
highest degree that the generative glands were developed in 
these Eurypterina posteriorly to the genital pores, and not 
anteriorly, as in Limulus. 
Further, the disposition of the eyes on such a quadran- 
gular carapace as that of Slimonia (fig. 20) is singularly 
like that seen in the Scorpion. Centrally are two small 
simple eyes, oc’, and precisely in the position which they 
occupy in Scorpion, viz. at the anterior lateral margin of the 
carapace, right and left, are groups of eyes, oc. In the 
Eurypterina, as in Limulus, these groups are close set in 
composition, so as to form what is called a compound eye, 
whereas in Scorpio the individual members of the group are 
separate. 
The individual factors of the compound eye of Limulus 
are more archaic in their histological structure than are the 
simple eyes of spiders, but at present we do not know the 
minute structure of the grouped eyes of Scorpio. It is 
possible that they may show closer agreement with the 
Limulus eye than do those of Spiders; or, again, it 1s not 
difficult to suppose that from a loose aggregation of very 
simple marginal eyes, which existed in the common ancestor 
of Limulus, Eurypterines, and. Scorpio, there has been de- 
veloped, on the one hand, by coalescence, the compound eye 
of the former; and on the other hand, by individual elabora~ 
tion, the separate eyes of the modern Arachnid. 
