22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



the claws and the tibia. This ring varies from a length equal tg about 

 a fourth that of the tibia to zero. Distally the two claws are inserted 

 into the membrane and about completely fill up the unchitinized space. 

 There is attached toi the unguitractor plate, which possibly is attached 

 to the ventral wall, the tendon of the flexor of the large claw, which 

 muscle may also in some instances lift the smaller claw. By compar- 

 ing the legs of various species it is observed that as this unguitractor 

 plate disappears the tendon of the flexor of the claws shifts over 

 until it comes to attach to the enlarged base of the large claw. Such 

 a shift indicates, it is believed, an obliteration of a tarso-pretarsal 

 articulation rather than the tibio-tarsal articulation. The tarsus, 

 therefore, has either fused with the big claw or has dropped out 

 entirely. The writer believes that in some instances it has done the 

 one and in others the other. 



The subcoxa not only frequently shows an external division into 

 two false segments, but many possess a transverse apodeme (pi. 6, 

 fig. 1 8, sex). 



THE COLLEMBOLAN TYPE OF LEG 



Although much variation is encountered in the legs of Collembola, 

 some of them being much modified and showing special adaptation 

 and some of them the loss of the tarsus, in general it may be stated 

 that they are of a very primitive type. The possession of a complete 

 and functional subcoxa and two typically articulated and muscled 

 trochanters is certainly a rare, primitive condition for the group 

 Insecta. While being of a primitive type the collembolan leg is of 

 somewhat unusual position and conformity. 



THE PRIMITIVE TYPE OE TARSAL CLAWS IN INSECTA 



The general l>elief among many entomologists has been that the 

 foot of a generalized insect possessed typically but a single claw. As 

 evidence for such a belief it has been pointed out that in certain prim- 

 itive insects, the Protura and certain springtails, there is but a sin- 

 gle tarsal claw. Also in most insect larvae and in centipeds such a 

 condition exists. It would appear, however, that much other evidence 

 is somewhat at variance to the one-claw theory. As pointed out by 

 Escherich (1910), the Lepismatidae have a three-clawed tarsus. 

 Many other Thysanurans also have the same type. As for the one- 

 clawed Collembola (pi. 7. fig. 19 B), such a condition is clearly sec- 

 ondary and not primitive. In all the two-clawed Collembola the second 

 claw is much reduced and modified (pi. 7, fig. 19, A), in many species 



