82 THE COCKROACH 



second maxillae. It is continuous with the chitinous integument of the neck. 

 Remove and draw the labium, noting its parts :— The broad shield-like base 

 divided by a transverse suture into a large submentum (the fused cardines), and 

 a distal smaller mentum (the fused stipites). To the mentum are attached 

 the free portions of the second maxillae, each consisting of the paraglossa 

 corresponding to the galea, the glossa corresponding to the lacinia, and the 

 three-jointed labial palp. The paraglossae and glossae together constitute the 

 ligula. 



A Walking Leg. 



Remove and draw the metathoracic leg of the left side, noting its parts : — 



(a) The coxa, the broad and flattened basal portion. 



(b) The trochanter, a small piece obliquely and almost immovably attached 



to the proximal end of the femur, on its inner side. 



(c) The femur, nearly straight and narrowed at both ends, and with a 



shallow longitudinal groove, fringed by stiff bristles, 'along its inner 

 border. 



(d) The tibia, longer than the femur, and armed with numerous stiff spines 



directed towards the free end of the limb. 



(e) The five-jointed tarsus, the proximal joint being the longest, while the 



distal joint, the pulvillus, bears a pair of equal and strongly curved 

 claws. 



Internal Structure. 



A. The Ahmentary System, and associated organs. 



Cut through the junction of the terga and sterna of the abdomen and the 

 thorax, and completely remove the terga, taking care not to injure the under- 

 Ijdng structures. Notice the tubular and chambered heart along the middle line 

 of the body, the diffuse white fatty body, and the silvery air-tubes or tracheae. 

 Carefully free the alimentary canal from the fatty body and the tracheae which 

 envelop it, and examine and draw the following parts : — 



The mouth opens into the buccal cavity, on the floor of which is a raised fold, 

 the lingua or tongue or hypopharynx. The ducts from a pair of salivary glands 

 with reservoirs open into the buccal cavity, which is continued into the oeso- 

 phagus. The oesophagus is a very narrow tube, laterally compressed in the neck, 

 but in the thorax it gradually expands into the very long and thin-walled crop, 

 which extends back into the abdomen. The crop is followed by a short conical 

 gizzard or proventriculus, with thick muscular walls, and containing six teeth 

 and six pads with setae. These aforenamed parts are lined with cuticle and 

 represent the fore-gut or stomodaeum. The narrow end of the gizzard leads 

 into the stomach (the mid-gut of mesenteron). The stomach is a simple tube, 

 provided, at its anterior end, with eight hepatic caeca which secrete a digestive 

 fluid ; and, at its posterior end, there are six bundles of very fine and long 

 Malpighian tubules, which are the excretory organs. Each bundle comprises 

 ten or more thread-like tubules, so that as many as sixty to seventy tubules may 

 be present. The stomach then leads into the small intestine or ileum, which is 

 followed by the large intestine, represented by the colon and the short rectum. 



