HANSEN AND SÖRENSEN: THE ORDER PALPIGRADI. 229 
out in what plane two joints move against each other by obser- 
ving the place of the condyli (or of the single condylus) in 
question, thereby determining the axis of the movement. Care 
must be taken, however, to see both condyli simultaneously — 
if both are present —, but this, of course, cannot be done with- 
out turning the limb in looking at it. So, this being impracti- 
cable under the microscope, we have paid special attention to 
the shape and outline of the articular membranes, to the shape 
of the joints and finally to the position of the muscles in the joint 
nearest to the articulation — beside each other or one above the 
other — and to the places above, below or at the sides to which 
the distal ends of the muscles are attached. Besides, we 
think we may trust to a certain extent that our many years 
acquaintance with the limbs of the Arachnids may have helped 
to enable us to form a correct estimate of the morphological 
value of tke joints. Between the joints which we designate as 
coxa and trochanter, femur and patella (or tibia, in the second 
pair of limbs), and tibia and metatarsus, the movement goes in 
a vertical plane, whereas between trochanter and femur, patella 
and tibia the movement is partly or essentially in a horizontal 
plane. We have noticed that at least some of the muscular 
fibres pass through the joints which, as far as we can see, move 
in a more or less horizontal plane, a fact which has confirmed 
the notion of the nature of the joints which we had previously 
acquired on another way. On this point we deviate somewhat 
from Grassi!" and we differ likewise with regard to the boundary 
line between the metatarsus and the tarsus. However, as to the 
last point we cannot insist with absolute certainty on the correct- 
ness of our view, as it is only based on a personal estimate. 
The Coxe (c) stand out freely in all the walking legs, so that 
they may be said to join the cephalothorax at their proximal 
end!! They are all somewhat compressed; as for the details 
Ur Gras is of the opinion that a patella is found in all the legs and 
that the metatarsus never consists of more than one joint. 
1 This character, however, we do not consider as being of much impor- 
tance, for while in the great majority of Arare@ the coxæ are united with 
the cephalothorax in a considerable part of their length, there are, we know, 
certain forms, as J/yrmecia, in which the coxæ are attached to the cephalo- 
thorax at their proximal end. 
