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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 80 



though in some other arthropod groups the muscles of the dactylopo- 

 dite arise in the propodite. 



The insect pretarsus is provided only with depressor muscles, called 

 usually flexor or retractor muscles of the claws, and in this feature 

 it resembles the terminal leg segment of the Chilopoda. In the 

 Crustacea, Pycnogonida, and Arachnida, however, the dactylopodite 

 has both levator and depressor muscles. Du Porte (1920) describes 

 an " extensor " of the claws in Gryllus, but here again his observation 

 is" clearly at fault. 



In insects and in the chilopods, the pretarsal muscles have their 

 origin in the leg segments proximal to the tarsus, and they are all 



Dae 



Dae 



Fig. 41. — Leg of proturan and of caterpillar, showing similarity of musculature. 



A, hind leg of Eosentomon gernianicum (Prell, 1912) ; B, right hind leg of 

 caterpillar of Estigmenc acraea, posterior view. (Lettering as on fig. 39, except 

 //, levator of femur.) 



inserted on a long " tendon "■ arising on the base of the pretarsus and 

 extending through the tarsus (fig. 39, x). In insects, the fibers of 

 the pretarsal muscles form several or numerous bundles (figs. 39, 40, 

 41, 43, X) arising in the tibia and the femur, and sometimes in the 

 trochanter, the number of the bundles and the points of their origin 

 varying much in different species. Where the pretarsus has the form 

 of a simple dactylopodite, as in Protura (fig. 41 A) and in certain 

 holometabolous larvse (figs. 41 B. 43), the apodeme, or "tendon," 

 of the pretarsal muscles arises directly froin its base — in Lepisma 

 it arises froin the base of the median claw (fig. 44 C, E, x) ; but in 

 other insects in which there is a special unguitractor plate, the tendon 

 arises from the proximal end of this sclerite (figs. 36 B, 39,44 B. Utr). 

 The pull of the muscles on the unguitractor plate turns the claws 



