XI APPENDAGES 2O7, 
behind. A small process or “ epicoxite” is found at the posterior 
end of the toothed part of the coxae of the second, third, fourth, 
and fifth pairs of appendages. The second appendage consists of 
seven joints, whilst the remaining four consist of eight joints; 
none of these appendages end in chelae. The second, third,’ and 
fourth pairs of appendages are similar to one another in structure, 
but become successively larger from before backwards. These 
three pairs are directed radially outwards ; each consists of short 
joints tapering to the end of the limb, and bearing spines at 
the sides and on the under surface, and also a spine at the end 
of the last joint. 
The fifth appendage is longer than the fourth and is directed 
backwards ; its second and third joints are short and ring-lke ; 
the others (fourth to eighth) are long and similar to one another, 
each being of uniform width throughout; the last joint is 
produced into a spine on each side, and between these two is the 
movable end-spine; the other joints do not bear long spines as 
is the case in the three preceding pairs.of appendages. 
The sixth appendage is much larger and stronger than the 
others, and like the fifth, is without long spines. The coxa is 
large and quadrate; the second and third joints are short, like 
those of the fifth appendage; the fourth, fifth, and sixth joints 
are longer and more or less bell-shaped; the seventh and eighth 
joints are much larger than the others and are flattened. 
The metastoma (Fig. 162, m) is an oval plate immediately 
behind the mouth; it covers the inner parts of the coxae of the 
sixth pair of appendages, and represents the chilaria of Limulus. 
But, unlike the latter, it is not a paired structure; nevertheless 
the presence of a longitudinal groove on its anterior part renders 
probable the view that it is derived from a paired organ.” The 
front margin of the metastoma is indented and toothed. On its 
inner side in front is a transverse plate, the endostoma, which 
is not seen from the exterior, since the front margin of the 
metastoma extends a little beyond it. 
Behind the prosoma are twelve free segments, of which the 
1 The third leg in the male possesses on the fifth joint a curved appendage 
which extends backwards to the proximal end of the second joint. This structure 
may have been a clasping organ. 
2 It has been suggested that the metastoma really belongs to a pre-genital 
segment of the mesosoma which is absent in the adult, but has been found in the 
embryo of Scorpions. 
