76 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



that the anterior muscle (p^) acts as a productor of the tarsus, and 

 the posterior muscle (pj) as a reductor when tension is exerted on 

 the muscles in a dead specimen. Morison (1927) calls these two 

 muscles anterior and posterior "extensors" of the tarsus, but if they 

 have an extensor effect on the tarsus, the action is weak. The third 

 tarsal muscle arises on the lower wall of the tibia (fig. 22 F, I, 94) 

 and is attached by an axial tendon in the ventral conjunctival mem- 

 brane of the joint. This muscle unquestionably is a depressor of the 

 tarsus. The opposite movement of the tarsus, if not produced by the 

 lateral muscles, must result from the elasticity of the articular con- 

 junctiva. In the fore leg the tibio-tarsal joint mechanism operates the 

 antenna cleaner. 



The tibio-tarsal joint of the hind leg, as above mentioned, differs in 

 some ways from that of the other legs. The articular condyle of the 

 basitarsus is a long, curved arm descending from the dorsal rim of 

 the proximal tarsal foramen (fig. 24 J, m) ; the corresponding articular 

 process of the tibia (I, m) is a strong sclerotization of the anterior 

 wall of the tarsal socket in the end of the tibia (L, m), which curves 

 inward over the tendon of the anterior muscle (114), dips downward, 

 and turns distally to articulate ventrally with the lower end of the 

 tarsal condyle (n). The articulation of the two segments is thus 

 almost at the center of the tarsal foramen. As a consequence, the 

 attachment of the posterior tarsal muscle (J, K, L, 7/5) is so far 

 above the level of the articulation that this muscle, representing the 

 tarsal reductor in the other legs, becomes in the hind leg a strong 

 levator of the tarsus. The anterior muscle (114), being inserted nearly 

 opposite the articular point, is evidently a productor ; the ventral 

 muscle (116) is the tarsal depressor. 



The structure of the tibio-tarsal joint of the hind leg is the same in 

 both the drone and the worker, and hence has no direct relation to the 

 pollen press of the latter. The mechanism of the joint in the hind 

 leg, however, especially the combined levator-productor action of the 

 two lateral muscles, is unquestionably conducive to the effective action 

 of the press. 



The tarsal joints. — The narrowed base of each of the small tarsal 

 subsegments, or tarsomeres, beyond the large basitarsus fits into a 

 receptive cavity in the end of the preceding tarsomere (fig. 23 G), 

 and each of these joints is monocondylic, as is the tibio-tarsal joint 

 itself. The dorsal lip of the minute basal foramen of each small 

 tarsomere is drawn out into a long articular process, which fits into a 

 socket formed by an inward extension of the lip of the distal foramen 

 of the tarsomere preceding. There are no intratarsal muscles giving 



