142 DESCRIPTIONS OF PREPARATIONS. 



stiff, semi-opaque, and coriaceous in texture. They act as wing-covers or tegmina, 

 and extend so far as to cover the fifth abdominal somite. Those of the second 

 pair are membranous and large : each wing has an anterior triangular area of stiff 

 texture and a thin posterior area. In repose, the base of the posterior portion 

 closes like a fan, and then the remainder of the wing is folded once lengthwise, the 

 edge of the fold being internal, the anterior firmer area of the wing lying uppermost 

 and protecting the thinner posterior area. In some Cockroaches the tip of the wing 

 is folded transversely. The base of attachment of both pairs of wings is broad. 

 In the female there is a pair of short tegmina, while the hind pair of wings is re- 

 presented only by two small triangular areae of the meta-notum marked by a few 

 ridges. Certain Cockroaches, e. g. Polyzosteria, are wingless in both sexes. 



The abdomen is flattened dorso-ventrally. Its outline is somewhat different in 

 the two sexes. It is made up of a number of distinct segments or somites, com- 

 posed each of a dorsal tergum and a ventral sternum connected at their margins by 

 a SQ&pleural membrane, hidden by the projecting free edges of tergum and sternum 

 alike. The portions of the terga and sterna exposed to light and air are hard and 

 dark, but the membranes which connect successive terga and sterna are colourless 

 and pliable. The first seven terga in both sexes are well developed, the 8 th and 

 9 th very narrow, and generally hidden by the y th ; the io* h is triangular and pro- 

 jecting. The i st sternum is rudimentary, and represented by a narrow band at the 

 base of the 2 nd sternum. This and the succeeding sterna to the 7*^ inclusive are 

 well developed in both sexes. In the male the 8 th and 9 th sterna are external, and 

 the last named has articulated to its free margin a pair of unjointed setose styles, 

 while the io th sternum is internal, and has developed in connection with it variously 

 shaped copulatory processes, which surround the aperture of the vas deferens. In 

 the female the 7 tn sternum is very large, and its posterior extremity is cleft medianly 

 in the adult (imago). The two halves are boat-shaped, and are connected by a 

 distensible soft skin. They retain the egg-capsule, which the female carries about 

 for a long time. The 8 th and 9 th sterna are internal, and bent at an angle inter se. 

 The 8 th has the vaginal aperture. There are three pairs of processes in connection 

 with these sterna, homologous with the parts of the oripositor in e.g. a Cricket, or 

 of the sting of a Bee. The first pair, according to Huxley, are developed from the 

 8th, the second and third from the 9 tlL sternum. The lo^ 1 sternum in the female 

 appears to be obsolete. The anus opens terminally in both sexes, and lies between 

 two triangular podical plates, probably representing an i i th somite, as in the Dragon- 

 fly. At the outer angles of these plates arise two many-jointed setose appendages, 

 the cerci anales, or cercopoda, supposed by Packard to represent a pair of rudi- 

 mentary abdominal legs. 



The nervous system consists of a supra-oesophageal ganglion supplying the 

 antennae, translucent white spots, eyes and labrum, and connected by very short 

 commissures to an infra-oesophageal ganglion supplying the mandibles, maxillae, and 

 labium. The ventral chain consists of three thoracic and six abdominal ganglia, 

 united by double commissures. The oesophageal commissures have under the 

 neurilemma a continuous layer of ganglion cells, and from them spring the two roots, 

 one on each side, of the ganglion frontale. The ventral commissures also contain 

 ganglion cells'. The stomatogastric system consists (i) of an azygos ganglion 

 1 According to Nussbaum a ridge of cells is developed from the hypoblast in the embryo Peri- 



