XIl] 



XIPHOSURA 



273 



plates termed the chilaria; these have been proved to be the 

 vanishing limbs of a vestigial segment. This segment appears in 

 the embryos of the Scorpion and the Spider, but is totally 

 suppressed in the adults of these animals. The next appendages. 



FIG. 124. Dorsal view of the King-crab, Limulns polyphemus x ^. 



3. Telson. 



Carapace covering prosoma. 2. 

 4. Median eye. 



Meso- and meta-soma. 

 5- Lateral eye. 



usually reckoned as the seventh, or the first on the mesosoma, 

 take the form of a flattened plate or operculurn which bears 

 the reproductive pores on its posterior surface. It is bent back and 

 underlies the eighth, ninth, tenth, eleventh, and twelfth pairs of 

 appendages, which are also plate-like and each of which bears on 



S. & M. 18 



