The fat-body is in reality, as development shows, the irregular cellular wall of the cœlom, or perivisceral space. Through this space courses the blood, flowing in no defined vessels, but bathing all the walls and viscera. In other words, the fat-body is an aggregation of little-altered mesoblast-cells, excavated by the cœlom, the rest of the mesoblast having gone to form the muscular layers of the body-wall and of the digestive tube. CHAPTER VI. THE NERVOUS SYSTEM AND SENSE ORGANS. _SPECIAL REFERENCES._ NEWPORT. Nervous System of Sphinx Ligustri. Phil. Trans. (1832–4). Todd’s Cyclopædia, Art. “Insecta” (1839). LEYDIG. Vom Bau des Thierischen Körpers. Bd. I. (1864). Tafeln zur. vergl. Anat. Hft. I. (1864). BRANDT (E.) Various memoirs on the Nervous System of Insects in Horæ Soc. Entom. Ross., Bd. XIV., XV. (1879). MICHELS. Nervensystem von Oryctes nasicornis im Larven--, Puppen--, und Käferzustande. Zeits. f. wiss. Zool., Bd. XXXIV. (1881). DIETL. Organisation des Arthropodengehirns. Zeits. f. wiss. Zool., Bd. XXVII. (1876). FLÖGEL. Bau des Gehirns der verschiedenen Insektenordnungen. Zeits. f. wiss. Zool., Bd. XXX. Sup. (1878). NEWTON. On the Brain of the Cockroach. Q. J. Micr. Sci. (1879). Journ. Quekett Club (1879). GRENACHER. Sehorgan der Arthropoden. (1879). [Origin, Structure, and Action of the Compound Eye.] CARRIERE. Sehorgane der Thiere, vergl.-anat. dargestellt (1885). [Comparative Structure of various Simple and Compound Eyes.] _General Anatomy of Nervous Centres._ The nervous system of the Cockroach comprises ganglia and connectives,[100] which extend throughout the body. We have first, a supra-œsophageal ganglion, or brain, a sub-œsophageal ganglion, and connectives which complete the œsophageal ring. All these lie in the head; behind them, and extending through the thorax and abdomen, is a gangliated cord, with double connectives. The normal arrangement of the ganglia in Annulosa, one to each somite, becomes more or less modified in Insects by coalescence or suppression, and we find only eleven ganglia in the Cockroach--viz., two cephalic, three thoracic, and six abdominal. [100] Yung (“Syst. nerveux des Crustacées Décapodes, Arch. de Zool. exp. et gén.,” Tom. VII., 1878) proposes to name _connectives_ the longitudinal bundles of nerve-fibres which unite the ganglia, and to reserve the term _commissures_ for the transverse communicating branches. [Illustration: Fig. 39.--Nervous System of Female Cockroach, × 6. _a_, optic nerve; _b_, antennary nerve; _c_, _d_, _e_, nerves to first, second, and third legs; _f_, to wing-cover; _g_, to second thoracic spiracle; _h_, to wing; _i_, abdominal nerve; _j_, to cerci.]