. Occasional papers of the California Academy of Sciences. at reduction in size and theydo not seem to have much locomotor importance inor out of galleries. In their normal position they ex-tend laterad and span a gallerys interior. They arecapable of great upward movement and frequentlythe tarsus of one of the pair is able to contact theupper surface of a gallery while the body is in a nor-mal position. It is possible that these legs aid rota-tion of the body within a gallery. The tarsi consist of elongated, unmodified seg-ments (Fig. 17C). The basal segment is evenly clothedventrally with st
. Occasional papers of the California Academy of Sciences. at reduction in size and theydo not seem to have much locomotor importance inor out of galleries. In their normal position they ex-tend laterad and span a gallerys interior. They arecapable of great upward movement and frequentlythe tarsus of one of the pair is able to contact theupper surface of a gallery while the body is in a nor-mal position. It is possible that these legs aid rota-tion of the body within a gallery. The tarsi consist of elongated, unmodified seg-ments (Fig. 17C). The basal segment is evenly clothedventrally with stout setae. The mid-tarsal segment issmall and has a distal papilla. In adult females andnymphs of many species, the ventral membrane ofthis papilla is clothed with very small, basally-directedpeg-setae which must aid reverse traction on the silksubstrate. In adult males this surface never is echinu-late and perhaps this is another indication of the malespoorer adaptation to gallery life. 24 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 149. Figure 20. A. Silk-ejectors (white) and combs of female Embia (SEM 440x). B. and C. Silk-ejectors and combs offemale Embia (SEM 1750x). Ejectors are highly variable in length and distal structure. Metathoracic legs Formerly, there was some question as to the func-tion of the greatly enlarged femora of the hind legs(Fig. 21). It was assumed that their enlargeinentindicated a saltatorial function. Davis (1936) exam-ined the tibial muscles and noted that, unlike saltato-rial insects which have large hind tibial extensor orlevator muscles, the flexor or depressor muscle isgreatly enlarged and thus accounts for the large sizeof the femora. The extensor, or levator, muscle ismuch reduced and fits into a groove atop the flexor(Fig. 21C, D). Such tibial musculature obviously facilitatesbackward movement in the galleries—an activity re-quiring strong muscles to flex the hind legs. Rapidreverse movement in narrow galleries has been a
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