244 



HARDWICKE'S SCIENCE-GOSSIP. 



is neither scent produced, nor track made in the 

 immediate neighbourhood by which an enemy 

 might have a clew to find it out and rob it of its 

 treasures. 



Waterton goes on to say these little wiles are 

 the very safety of the nest, and he suspected that 

 they are put in practice by most birds that have 

 their nests on the ground ; and to this circumstance 

 he attributes the great increase of his pheasants by 

 not allowing them to be disturbed, though they 

 were surrounded by hawks, jays, crows and mag- 

 pies, which had large families to maintain and 

 bring up in the immediate neighbourhood. 

 ( To be conti fined. ) 



THE NERVOUS SYSTEM OF THE 

 COCKROACH.* 



By Professor L. C. Miall and Alfred Denny. 



THE nervous system of the cockroach comprises 

 ganglia and connectives,! which extend 

 throughout the liody. We have, first, a supra- 

 cesophageal ganglion, or brain, a sub-oesophageal 

 ganglion and connectives which complete the oeso- 

 phageal ring. AH these lie in the head ; behind 

 them, and extending through the thorax and abdo- 

 men, 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 

 cejihalic, three thoracic, and six abdominal. 



The nervous centres of the head form a thick, 

 irregular ring, which swells above and below into 

 ganglionic enlargements, and leaves only a small 

 central opening, occupied by the oesophagus. The 

 tentorium separates the brain or supra-oesophageal 

 ganglion from the sub-ccsophageal, while the con- 

 nectives traverse its central plate. Since the ceso- 

 phagus passes above the plate, the investing nervous 

 ring also lies almost wholly above the tentorium. 



The brain is small in comparison with the whole 

 head ; it consists of two rounded lateral masses or 

 hemispheres, incompletely divided by a deep and 

 narrow median fissure. Large optic nerves are 

 given off laterally from the upper part of each 

 hemisphere ; lower down, and on the front of the 

 brain are the two gently rounded antennary lobes, 

 from each of which proceeds an antennary nerve ; 

 while from the front and upper part of each hemi- 

 sphere a small nerve passes to the so-called " ocellus," 



* For the " Natural History, Outer Skeleton, Alimentary 

 Canal, and Organs of Respiration and Circulation of the Cock- 

 roach," see this Journal, March, May, July, and September, 

 1884. 



f Mons. Yung (" .Syst. nerveux des Crustacees decapodes. 

 Arch, de Zool. exp. ct gen.," toui. vii. 1878) proposes to name 

 (-oniiectivL'S the longitudinal bundles of nervc-iibres which unite 

 the ganglia, and to reserve the term cominissurcs for the 

 transverse communic.iting brrnches. 



a transparent spot lying internal to the antennary 

 socket on each side in the suture between the clypeus 

 and the epicranium. The sub-oesophageal ganglion 

 gives off branches to the mandibles, maxillae and 

 labruni. While, therefore, the supra-cesophageal is 



xo/ 



Fig. 144. — Nervous system of female Cockroach, X 6. a, optic 

 nerve; b, antennary nerve; c, d, e, nerves to lirst, second, 

 and third legs ; /, to wing-case ; g^, to second thoracic spi- 

 racle ; h, to wing ; i, abdominal nerve ; j, to cerci. 



largely sensory, the sub-cesophageal ganglion is the 

 masticatory centre. 



The oesophageal ring is double below, being com- 

 pleted by the connectives and the sub-oesophageal 

 ganglion ; also by a smaller transverse commis- 



