AETHROPODA 273 



2. Abdomen. 



Number of segments (differs in male and female). 

 Dorsal and ventral plates. Are they equally developed in 



all segments. 

 Appendages: which segments possess them? 



Ovipositors (paired outgrowths found only in the female). 



Anal cerci (examine the male). Are they found in the 



female? To what segments do these appendages 



belong ? 



Spiracles (small openings at the side of the segments) ; 



number and distribution ? 

 Tympanic membrane, at the sides of the first abdominal 

 segment. 



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. 

 Genee, the lateral plates. 

 Labrum or upper lip, anterior to the clypeus. 

 Examine the compound eyes, their form and relation to the 

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

 surface with a low-power objective. 

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

 Mouth aperture; position. 

 Appendages of the head : 



Antennae, near the eyes; number. 

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