XVII EXTERNAL FEATURES 443 
is long and narrow in the Mecostethi, and Cyphophthalmi, but 
in the Plagiostethi, which include most of the forms found in 
temperate regions, it is very short 
and transverse, and is hidden by 
the abdominal prolongation before 
mentioned. 
The anterior wall of the mouth 
is formed by a beak-like plate, the 
“epistome,’ the basal portion of 
which is covered externally by a 
second plate, for which Simon! pro- 
poses the name “ pre-epistome.” In 
some Phalangids there are three little 
chitinous plates, one median and two 
lateral, on the clypeus, between the 
anterior border of the carapace and 
the insertion of the chelicerae. They 
are best seen in Nemastoma. 
The abdomen always presents 
pre.cp. 
> ped. 
Fic. 231.—Mouth-parts of Phalan- 
gium. A, B, C, Gnathobases of 
pedipalp and first and second 
legs ; ch, chelicera ; ep, epistome ; 
lab, \abium; m, mouth ; ped, 
pedipalp ; pre.ep, pre-epistome ; 
st, sternum, shown by the removal 
of the anterior part of the genital 
process, which extends to the 
dotted line; 1, 2, 3, 4, legs. 
evidences of segmentation, though 
there is a difference of opinion as to the number of segments 
of which it is composed. This is due to the already mentioned 
partial or complete fusion of the anterior segments with the 
cephalothorax. From the admirable researches of Hansen and 
Sérensen ? it seems likely that the normal number of abdominal 
segments is ten. Ventrally, the abdomen is produced forward 
into a “sternal process” which is capped by a genital plate, 
hardly distinguishable in the Phalangidae, but readily visible 
in the other families, which surrounds and masks the unpaired 
genital orifice. Two stigmata or breathing pores are situated on 
the sides of the first ventral plate, which these authors consider 
to be composed of two fused sternites. 
As in other Arachnids there are six pairs of appendages 
articulated to the cephalothorax. They are the chelicerae, the 
pedipalpi, and the four pairs of ambulatory legs. 
The chelicerae are three-jointed and chelate, the second joint 
having its inner portion produced into an apophysis to which 
the final joint is apposed. In certain forms (Gonyleptidae, 
1 Arachnides de France, vii., 1879, p. 122. 
2 On two Orders of Arachnida, Cambridge University Press, 1904. 
