198 



PSYCHE. 



[May, 1901. 



distally in four prominent, equidistant 

 teeth, with the convex posterior face 

 thickly set with hairs and a row of 

 stouter hairs or spinules on the outer 

 margin, the tarsus being inserted be- 

 tween the first and second teeth and 

 lying on the anterior face. In three of 

 the others, while the structure remains 

 similar, the outline of the tibia has 

 become subtriangular through the pro- 

 duction of the inner side of the distal 



Tridnctybts teniiiitalis Scudd. Left anterior leg viewed 

 from beliind. Fig. t. Female. Fig. 2. Male. Fig. 3. Male 

 Fig. 4. Male. Fig. 5. Male ; tibia closed upon tlie 

 femur. 



end (Fig. 2); in addition to this, there 

 is a slight but distinct deepening of the 

 fissure between the second and third 

 teeth. This lengthening of what may 

 be called the iimer limb of the tibia and 

 deepening of the emargination between 



the inner and outer limbs is exhibited by 

 all the remaining specimens in progres- 

 sive degree until we have a remarkably 

 bifurcate organ (Figs. 4, 5) whose rela- 

 tion to the normal form would be made 

 out with difficulty but for the series of 

 connecting gradations. 



In addition to this bifurcation and the 

 elongation of the inner limb, the latter 

 loses its hairy covering, the innermost 

 tooth nearly disappears, the second is 

 greatly prolonged into a backwardly 

 directed claw-like organ, the third and 

 fourth teeth (on the outer limb) become 

 enlarged and produced, the angle be- 

 tween the two limbs becomes greater 

 and greater, and the femur acquires 

 tooth-like protuberances on its proximal, 

 inner, ventral angle and becomes great- 

 ly enlarged (Figs. 1-5). The gradation 

 is so perfect (even in this relatively 

 small series of examples) that it is im- 

 possible to draw any sharp line of de- 

 marcation between the specimens ; some- 

 times, even, the right and left tibiae of 

 the same insect are appreciably dift'erent 

 in form. C)f the t,t^ males, in ten the 

 tibia is of normal ( 9 ) form ; in three 

 others it is slightly but perceptibly modi- 

 fied, in one it is intermediate between 

 Fig. I and Fig. 2, in two it is of the form 

 of Fig. 2, in two intermediate between 

 Fig. 2 and Fig. 3, in four like Fig. 3, in 

 one midway between Fig. 3 and Fig. 4, 

 in four but little less modified than in 

 Fig. 4, and in six it has the form of Fig. 

 4 (open) and Fig. 5 (closed), the greatly 

 elongated second tooth varying much in 



