LIMULUS AN ARACHNID. 513 
origin in the large nerves supplying the appendages, or the 
genital or the respiratory region, which can forbid us from 
unreservedly accepting as exactly representing one another, 
parts, which on the ground of numerical sequence, appear to 
reciprocally correspond. 
§ 6. SKELETON.—I. Tergites, or Dorsal Sclerites.—It is 
difficult to separate the description of one part of the skeleton 
OC -.-/..... 
eA rine es XIV to XVIIl 
Anus 
Fie. 1.—Outline of the tergal surface of Limulus polyphemus (drawn from the 
object). The dotted lines correspond to the markings on the abdo- 
minal carapace, which in the adult indicate what were separate segments 
in the embryo. 4c’. Simple eyes (mesial). oc. Compound, or grouped 
eyes (lateral). 2.4. Post-anal spine. 
of Limulus and Scorpio from that of another, and in com- 
