APPENDAGES 287 



behind. A small process or " epicoxite " is found at the posterior 

 end of the toothed part of the coxae of tlie 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-like ; 

 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, Tinlike 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, wdiich 

 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 



' 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. 



