Dissected to show its digestive, renal, nervous, and reproductive systems.
AMONG external features characteristic of the class Insecta, the head with the antennae, the three pairs of jointed thoracic limbs, and the segmented abdomen may be noted. The short tegmen or wing-cover of the female of this species is visible above the second limb on the right side, and posteriorly, on the same side also, at the extremity of the abdomen, one of the two short jointed cerci anales found in many Orthoptera, etc.
The dorsal body walls or terga, and the fat body which abounds between the viscera, especially in the abdomen of these insects, even in their adult state, have been removed, and the digestive tract fastened out upon the left side of the body.
The digestive tract is divisible into three regions, which correspond to the stomodaeum, archenteron, and proctodaeum of the embryo. The first of these includes oesophagus, crop and gizzard, the second, the chylific stomach and caeca, and the third, the intestine and rectum. The narrow oesophagus expands directly into the crop, which occupies about three-fourths of the entire length of the body, and is distended with food. The digestive tract as a whole, however, is little more than twice as long as the body, a comparative shortness compensated partly by the character of the food, and partly by the large quantities devoured. A muscular subconical gizzard follows the crop. This organ is not developed in the larvae of In-secta with a perfect metamorphosis, e. g. Coleoptera, in those species which possess it when adult, but is developed in larval Orthoptera as well as Odonata. The posterior end of the gizzard is elongated and projects into the chylific stomach. Eight 'pyloric' caeca arranged in a whorl mark the commencement of this region, and a very much larger number of long and slender Malpighian or renal tubes its termination. Pyloric caeca are found in most Orthoptera, and in the Plecoptera. Their walls are glandular, and the size of the caeca varies with their state of distension.
The intestine consists of a short, narrow 'ileum,' and a long, somewhat dilated colon. The ileum is not clearly visible in this preparation. The colon is ridged and beaded owing to the contraction of its muscular coats. It ends in a rectum, which shows six longitudinal ridges alternating with furrows.
The lobed labial salivary glands are to be seen on either side of the anterior end of the crop: and on the right side in this preparation the right salivary receptacle, a .pellucid bladder reaching a little further back than the gland.
An azygos nervus recurrens, derived from the 'ganglion impar' or 'frontale' of the stomatogastric system, lies on the dorsal wall of the crop, and ends in a triangular ganglion placed a little way in front of the middle point of its length. From this ganglion a nerve may be traced passing down the sides of the crop to the gizzard. The paired ganglia of the system are not to be seen. The six terminal ganglia of the ventral chain are visible in the abdomen. The two first are more closely apposed to each other than are any of the succeeding four. The last ganglion is more or less cordiform, larger than those which precede it, and gives off nerves to the lower portion of the digestive and generative tubes.
Each ovary consists of eight ovarian tubes or ovarioles inserted in pairs, on the inner edge of the oviduct, one set of tubes along its ventral, the other on its dorsal margin. The tubes are beaded, owing to the swellings caused by the ova. These ova increase in size the nearer they are to the oviduct. The tips of the ovarioles are in the natural state united by short filaments to a common ligament. This ligament is probably attached, as in other Insecta, near the heart. The two oviducts open beneath the last ganglion of the ventral chain into a short vagina. The spermatheca consists of a short peduncle terminated by two slightly curled vesicles. It opens into the vagina behind the last nerve ganglion. And opening in turn behind it are the right and left colleterial glands, often, but wrongly, termed sebaceous. They secrete the material which forms the cocoon.
The Cockroach, according to Cornelius, moults seven times before it becomes adult. The first moult occurs immediately after hatching; the second a month later; and the remaining moults at intervals of a year. The adult stage is reached in the fifth year. The young animal differs from the adult principally by inferiority of size, by the smaller number of facets in the cornea of the eye, by the absence of wings, imperfection of the genitalia, and in this family by lightness of colour, a feature, however, in which great differences exist between adult individuals of this species. The absence of a quiescent stage and of a period of abstention from food, such as exist in Insecta with a perfect metamorphosis, is probably the reason why the fat body persists, instead of being utilised as a storehouse of force during the internal changes undergone by the organism.
A Gregarine Clepsidrina blattarum is often found in the body cavity of the Cockroach, and some remarkable Flagellate Protozoa in its intestine.
The body is divisible, as in all adult Insecta, into a head, thorax, and abdomen.
The head is broad transversely, and compressed antero-posteriorly. It is carried vertically, not horizontally as in many forms. Its dorsal surface or Epi-cranium is convex, and is marked by a Y-shaped epicranial suture, as in the Earwig. This suture is in some specimens indistinct. The branches of the Y end in a translucent spot of unknown function placed superiorly to the inner side of the articulation of the antennae. The front of the head (= clypeus) is flat and broad, and a labrum is moveably articulated to it, closing in the mouth anteriorly. The antennae are long, filiform and many jointed. The joints are beset with hair (i.e. are setose), and the basal joint is attached to a soft membrane, which closes the socket. For the minute anatomy of antennae, see p. 145, infra. Behind the antennae are the reniform compound eyes. There are no ocelli.