ARTHROPODA. 269 



3. Thorax ; studying from the front, backward, find : 

 Prothorax; mesothorax; metathorax. Note the form, 



size, and structure of each part. 

 Appendages of each segment. 



Legs: number; relative size; parts (beginning at the 

 body), coxa, trochanter, femur, tibia, tarsus. Com- 

 pare the legs. 



Wings (can these be regarded as homologous with 

 the jointed appendages?) : number; position, at rest 

 and in motion ; characteristics ; position of veins. 

 Compare the two pairs in all essential particulars. 

 Are there any spiracles in the thorax? Position? 



4. Head (is there any "neck"?). The head is covered 

 with chitinous plates; identify: 



Epicranium, the dorsal plate. 



Clypeus, the anterior plate. 



Gense, the lateral plates. 



Labrum or upper lip, anterior to the clypeus. 

 Examine the compound eyes, their form and relation to the 



plates. Slice off a portion of the surface and study the 



surface with a low-power objective. 

 Ocelli or simple eyes. How many and in what position? 

 Mouth aperture; position. 

 Appendages of the head : 



Antennae, near the eyes; number. 



Mouth-parts. These are complicated and demand careful study, if 

 satisfactorily made out. Remove the labrum and proceed from 

 before, backward. 



Mandibles; a pair of horny tooth-bearing jaws. Draw in position. 



Maxilla; a pair of compound jointed organs made up of three 



portions, the lacinia (nearest the median line), the galea, and 



the maxillary palpus (external). 



Labium or lower lip ; this also bears a palpus. The labium may 



be studied and removed before the study of the maxillae. 

 Tongue. 



How many segments seem to be represented in the head? 

 Internal structure. 



Select large female specimens preferably. Clip the wings close to 

 the body, and pin the specimen to a board, dorsal surface upward. 



