HA RD WICKE'S S CIENCE- G OS SI P. 



245 



sure, which unites the connectives, and applies itself 

 closely to the under surface of the oesophagus.* 



Two long connectives issue from the top of the sub- 

 cesophageal ganglion, and pass between the tentorium 

 and the submentum on their way to the neck and 

 thorax. The three thoracic ganglia are large, in 

 correspondence with the important appendages of 

 this part of the body, and united by double connec- 

 tives. The six abdominal ganglia have also double 

 connectives, which are bent in the male, as if to avoid 

 stretching during forcible elongation of the abdomen. 

 The sixth abdominal ganglion is larger than the rest, 

 and is no doubt a complex, representing several 

 coalesced posterior ganglia; it supplies large branches 

 to the reproductive organs and rectum. 



In the cockroach the stomato-gastric nerves found 

 in so many of the higher invertebrates are conspicu- 

 ously developed. From the front of each oesophageal 

 connective, a nerve passes forwards upon the 



Fig. 145. — Side-view of brain of Cockroach, X 25. op, optic 

 nerve ; oe, oesophagus ; t, tentorium ; sb, sub-oesophageal 

 ganghon ; w«, w.r, mx', nerves to mandible and maxillae. 

 [Copied from E. T. Newton.] 



surface of the crop ("3 inch from the ring), in a 

 triangular ganglion, from which a nerve is given off 

 outwards and backwards on cither side. Each nerve 

 bifurcates, and then breaks up into branches which 

 are distributed to the crop and gizzard.* Just 

 behind the oesophageal ring, the recurrent nerve 

 forms a plexus with a pair of nerves which proceed 

 from the back of the brain. Each nerve forms two 

 ganglia, one behind the other, and every ganglion 

 sends a branch inwards to join the recurrent nerve.. 



J U V 



-J'' [/■ 



Fig. 146. — Stomato-gastric nerves of Cockroach. />■■£■, frontal 

 ganglion; at., antennary nerve; conn., connective; pi.g-, 

 paired ganglia ; r. n., recurrent nerve ; v. g., ventricular 

 ganglion. 



oesophagus, outside the chitinous crura of the ten- 

 torium. Each nerve sends a branch downwards to 

 the labrum, and the remaining fibres, collected into 

 two bundles, join above the oesophagus to form a 

 triangular enlargement, the frontal ganglion. From 

 this ganglion a recurrent nerve passes backwards 

 through the oesophageal ring, and ends on the dorsal 



* This commissure, which has been erroneously regarded as 

 characteristic of Crustacea, was found by Lyonnet in the larva 

 of Cossus, by Strauss-Durckheim in Locusta and Buprestis, by 

 Blanchard in Dytiscus and Otiorhynchus, by Leydig in Glo- 

 meris and Telephorus, by Dietl in Gryllotalpa, and by Lienard 

 in a large number of other Insects and Myriapods, including 

 Periplaneta. See Lienard, "Const, de I'anneau cesophagien," 

 Bull. Acad. roy. de Belgique, 2me sdr. t. xlix. 1880. 



Fine branches proceed from the paired nerves of the 

 (esophageal plexus to the salivary glands. 



The stomato-gastric nerves differ a good deal in 

 different insects ; Brandt f considers that the paired 

 and unpaired nerves are complementary to each other, 

 the one being more elaborate, according as the other 

 is less developed. A similar system is found in 

 mollusca, Crustacea, and some vermes (e.g., Nemer- 

 teans). When highly developed, it contains unpaired 

 ganglia and nerves, but may be represented only by 



* The stomato-gastric nerves of the cockroach have been 

 carefully described by Koestler (," Zeitsch. f. wiss. Zool.," 

 Bd. xxxix. p. 592). 



t " Mem. Acad. Petersb.," 1835. 



