24 A GUIDE FOR THE STUDY OF ANIMALS 



or somites into which the thorax of any insect is divided. 

 A pair of legs is borne on each division. 



Exoskeleton, an external skeleton. 



Femur, tibia, and tarsus, the three principal divisions of 

 the leg corresponding to thigh, shank, and foot. 



Veins, thread-like thickenings of the wings. 



Ocelli, the single or simple eyes of an insect, composed 

 of a single eye element. 



Compound eyes, made up of many eye elements. 



Auditory sacs, organs for hearing in many animals. 



Antennce, the feelers borne on the head. 



Labrum, the upper lip. 



Labium, the lower lip, formed by the growing together 

 of the second maxillae. 



Mandibles, primary jaws situated under the labrum. 



Maxillce, secondary jaws just in front of the labium, 

 each composed of three parts, a palp, a spoon, and a 

 tooth. 



Palps, the jointed finger-like structures used to handle 

 food, one pair on the labium and one pair on the maxillae. 



Spiracles, openings into the trachea found along the 

 sides of the abdomen and thorax. 



Trachea, slender tubes used for breathing organs among 

 insects. They carry the air direct to the tissues in all 

 parts of the body. 



Ovipositors, structures on the posterior end of the abdo- 

 men of a female, used to deposit eggs. 



Metamorphosis, refers to the development of the young 

 of animals when striking changes in structure occur in the 

 course of their growth. Metamorphosis is called com- 

 plete when the young have no resemblance to the adults, 

 and incomplete when there is a resemblance to the adult. 

 In complete metamorphosis the stages are larva, pupa, and 



