I4<S MORPHOLOGY OF INVERTEBRATE TYPES 



epicranium. The front of this capsule is called frons, the back, 

 occiput, the top, vertex, and the two sides cheeks or gena. A 

 plate attached to the lower end of the frons and itself serving 

 for the attachment of the upper lip or labrum is called clypeus. 

 Thorax and its appendages. The thorax is composed of 

 three distinct somites. The first thoracic somite is called the 

 prothorax and carries the first pair of legs. The integument of 

 the prothorax forms a large dorsal sclerite or tergite usually 

 known under the name of pronotnm. The corresponding ven- 

 tral sclerite or prosternum carries a spine. The head is joined 

 movahly to the prothorax as the prothorax itself is joined mov- 

 ably to the second thoracic somite or mcsothorax. The meso- 

 thorax is joined immovably to the third thoracic somite or meta- 

 thorax. This is due to the presence of a deep incision in the 

 posterior margin of the mesosternum into which a corresponding 

 process of the metathorax fits perfectly. The posterior edge of 

 the latter has a similar incision for the reception of a process of 

 the first abdominal sternite. The mesothorax has a pair of legs 

 and a pair of wings which in this case are modified as covers for 

 the real wings of the following somite. The metathorax has a 

 pair of legs especially adapted to jumping and a pair of wings 

 which are thin and folded under the covers when not in flight. 

 Both meso- and metathoracic wings are simple outgrowths of 

 the integument and the "veins" of the wing are thickened por- 

 tions having the structure of a tube. The cavity of the veins 

 incloses special nerves and tracheal tubes and communicates 

 directly with the body cavity. The arrangement of the "veins" 

 or the so-called venation of the wings follows a definite plan 

 which is of great importance for a comparative study of insects. 

 The legs consist of five segments, the coxa by which it is attached 

 to the body, the Irochanter a short segment corresponding to 

 the ischiopodite, the femur (or meropodite), the tibia (a fused 

 carpo and propodite) and a three-jointed tarsus or dactylopodite. 

 The ventral surface of the first joint of the tarsus is subdivided 

 by pads giving it the appearance as if it were composed of 



