522 PROFESSOR E. RAY LANKESTER. 
In Scorpio the third cephalothoracic appendage is in the 
form of a walking leg, and as such has seven sclerites. It 
is a remarkable fact that in Limulus the sixth cephalo- 
thoracic appendage, which is non-chelate, also presents 
seven axial sclerites (woodcut, fig. 4, v1, right), so that the 
Scorpion’s ambulatory limbs do not depart from the possi- 
bilities of Limulus in developing axial sclerites beyond the 
number six. It isalsoimportant to notice in this connection 
that the Arachnida exhibit a great variability in the number 
of joints present in their legs. 'Thelyphonus develops a four- 
jointed “tarsus” at the end of the five proximal segments 
of its ambulatory limbs (woodcut, fig. 12), whilst Galeodes 
presents ‘a curious increase in the number of segments in 
the proximal region of its hinder limbs (woodcut, fig. 10). 
The most important feature in which the third and sub- 
sequent cephalothoracic limbs of Scorpio resemble those of 
Limulus is in the great development of the coxe. The 
sterno-coxal process is present on the third and fourth 
cephalothoracic appendages, and is even larger relatively than 
in Limulus. In the third and fourth limbs it is free, overlying 
a very soft minute sternal region belowthe mouth, and playing 
with its fellow of the opposite side the part of an ingestive 
organ for the mouth. The narrow cleft between the opposed 
sterno-coxal processes probably acts by capillary attraction 
in the taking up of such food as the blood of other animals. 
The coxe of the fifth and sixth appendages of Scorpio 
have, on the other hand, no free sterno-coxal process. 
The great enlargement of the coxe of these four pairs of 
appendages, and their encroachment upon the median area, 
is accompanied by, and related to, the suppression of any 
representative of the sternal sclerite (pmst., fig. 4, 
Pl. XXVIII) which is present in Limulus. The coxe of 
the third pair and of the fourth pair meet one another in 
the middle ventral line, but are separated by soft membrane. 
The cox of the fifth and sixth pairs do not meet their 
fellows in the middle line, but are kept apart by the wedge- 
shaped extremity of a sternite (met. in woodcut, fig. 8). 
They differ from the coxze of the third and fourth pairs in that 
the fifth is adherent to the sixth (woodcut, fig. 4, v, v1, left.) 
The base of the third appendage in Scorpio exhibits a 
development internal to the sterno-coxal process, which 
corresponds to, and probably represents, the ‘‘ epicoxite ” of 
Limulus. This is in the form of a movable plate (woodcut, 
fig. 4, 111, epe., left), which presents parallel ridges on its 
surface. 
Cephalothoracic appendage, No. IV.—Appendage No. iv 
