Key: So. = Supra-oesophageal. Si. = Supra-infundibular. Io. = Infra-oesophageal. Ii. = Infra-infundibular. Ps. = Prosomatic. Ms. = Mesosomatic. +---+--------------------------------------------------------+ | | Median Eyes. | | +--------------------------------------------------------+ |So.| Lateral Eyes. | | +--------------------------------------------------------+ | | Camerostome. | +---+--------------------------------------------------------+ | | Invertebrate (Limulus or Eurypterid). | +---+---+---------+-----------------------------+------------+ | | | | Appendages. | Coelomic | | | |Segments.+-------------+---------------+ Cavities. | | | | | Limulus. | Eurypterid. | | | | +---------+-------------+---------------+------------+ | | | 1 | Cheliceræ | Cheliceræ | 1 | | | +---------+-------------+---------------+------------+ | | | 2 |1st Locomotor|} | | | | +---------+-------------+} | 2 | | | | 3 | 2nd " |} |Ventral part| | |Ps.+---------+-------------+}4 Endognaths | forms coxal| | | | 4 | 3rd " |} | gland. | | | +---------+-------------+} | | | | | 5 | 4th " |} | | | | +---------+-------------+---------------+------------+ |Io.| | 6 | 5th " | Ectognath | 3 | | | | | | | | | | +---------+-------------+---------------+------------+ | | | 7 | Chilaria | Metastoma | 4 | | | | | | | | | +---+---------+-------------+---------------+------------+ | | | 8 | Operculum |Genital } | 5 | | | |---------+-------------+ }Oper-+------------+ | | | 9 |1st Branchial| }culum| 6 | | | | | |Branchial} | | | |Ms.+---------+-------------+---------------+------------+ | | | 10 | 2nd " | 2nd Branchial | 7 | +---+---+---------+-------------+---------------+------------+