l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



THE COXAL APPENDAGE IN SYMPHYLA 



The coxal appendage in Symphyla arises in nearly all the species 

 from the coxa on its inner side very near the articulation of the latter 

 with the body and the subcoxa. In a few species it arises from the 

 body proper near the origin of the coxa, but in such instances moves 

 with the coxa. It is a small, slender, cylindrical appendage, and is 

 clothed with minute setaHke projections (pi. 5, fig. 12). On the tip 

 of the appendage these setalike structures are longer than the width 

 of the appendage, but on the body of the latter are only visible with 

 very high magnification. The writer has not studied stained sections 

 of symphylids, but since these setalike structures lack seta pits he 

 is inclined to consider them as scobinations. It is possible that the , 

 longer terminal ones are different from the minute lateral ones, in 

 which case they should be regarded as true setae. 



All efforts to locate muscle fibers passing to the coxal appendages 

 have failed, although such fibers do pass from the body wall to the 

 chitinous base ring of the eversible sac. 



In the Lepismatidae Escherich (1905) has found muscle fibers 

 passing both to the eversible sacs and the styli of the abdomen. It is 

 probable that the coxal appendages in Symphyla are not true seg- 

 mental appendages. They may or may not be homologous with the 

 coxal appendages in Pauropoda and Machilidae. Their position on 

 the inside of the coxa indicates a homology with the appendages of 

 Pauropoda rather than with those of Machilidae, which are external. 



THE LEGS IN THYSANURA 



The Thysanura have long been an interesting group for the student 

 of the phylogeny of insects. Their primitive wingless condition, their 

 possession of vestigial abdominal appendages and several other mor- 

 phological characters have stamped them as an outstanding gen- 

 eralized group among their class. 



An examination of the legs of each of the four families of Thysa- 

 nura, the Machilidae, Lepismatidae, Japygidae and Campodeidae 

 shows that they all have the same type of segmentation and muscu- 

 lature and the same number of true segments. For this reason the 

 leg of Machilis, the first to be here considered, may be taken as a 

 type. Borner (1921) has described the musculature of Machilis. 



In Machilis the first movable segment of the leg (pi. 5, fig. 13) is 

 the largest. It has the general shape of a femur but is placed in a 

 reverse position, i. e., it hangs downward and outward from the 

 body. At about one-third the distance from its proximal to its distal 



