20 Annals Entomological Society of America [Vol.11, 



enclosed in the trochanter. Such conception is certainly true in 

 the case of the flexor bilobatus. As for the flexor femoris longus, 

 some doubt may be expressed as to its homology- with the corres- 

 ponding flexors of the patella and metatarsus. But the short- 

 ness of the trochanter and the difl'erence in articulation may be 

 held responsible for the fact that the flexor femoris longus arises 

 from another surface than its homologs. The muscles of the pa- 

 tella are doubtless homologous with those of the coxa with that 

 exception that there is no extensor tibiae. We must however 

 remember that an extensor tibiae would be of still less use than 

 the flexor, since the patella has a special tooth at its distal end 

 interlocking with the tibia. This interlocking device prevents 

 the tibia from being raised apart from the patella, the only func- 

 tioning "knee" articulation being that between the femur and 

 the patella. 



EXPLANATION OF THE FIGURES (PLATE IV.) 



1. Diagram of a spider showing the axis of complex symmetry, AP, and 

 the planes of symmetry of the legs, pd, and of the chelae. The second and 

 third legs on the right side are removed. The figure represents the dorsal sur- 

 face of the spider and the legs are extended in such a manner that the surface 

 of the paper represents the episynaxial surface. 



2. Diagram representing a cross section of the leg of Pholcus phalangoides. 

 EH, the plane of symmetry. It is understood that the observer sees the cross 

 section in looking from the body of the spider towards the end of the leg. In 

 consequence it is evident from the letters accompanying the diagram that it is 

 a cross section of a right leg. In a left leg the two halves are reversed. ESP, pro- 

 episynaxial ; ESR, retoepisynaxial ; EP, apipro, ER, epiretra; MP, middle pro; 

 MR, middle retro; HP, hypo pro; HR, hyporetro hair. 



3. The muscular system of a spider leg. fi. tr. , flexor trochanteris; ex. tr. , 

 extensor trochanteris; r. tr. , retractor trochanteris. Its antagonist, the M. pro- 

 motor trochanteris, runs parallel to the retractor and cannot therefore be repre- 

 sented on the diagram. One inust imagine that it was removed for the purpose 

 of showing the other muscles, fi. f . 1. , flexor femoris longus ; fl. f . b. , flexor fe- 

 moris bilobatus; fl. p. 1., flexor patellae longus; fl. p. b., flexor patellae bilobatus; 

 fl. t., flexor tibiae; r. t. , retractor tibiae. Its antagonist the M. promotor tibiae 

 runs parallel to the retractor and could not be represented in the diagram, 

 fl. m. 1., flexor metatarsi longus; fl. m. b., flexor metatarsi bilobatus; flu., flexor 

 unguium; ex. u., extensor unguium- tn. f. , the tendon of the flexor; tn. c, the ten- 

 don of the extensor. 



4. The bristles surrounding the claws of Pholcus phalangoides. The 

 heavy upper and lower bristles are single. Three bristles corresponding with 

 the three other bristles of the figure are situated on the other side of the claws 

 and can not be represented. 



5 — 11. Hairs on the legs of Pholcus phalangoides. 5, on femur, patella, 

 tibia and the two proximal thirds of metatarsus. 6, a part of the same hair 

 stronger magnified. 7, a hair from the distal end of the metatrasus; 8, a hair 

 from the tarsus. 9, the combhair of the fourth tarsus. 10, one of the few 

 erect, scattered hairs on the tarsus. 11, the same from the metatarsus. 12, one 

 of the combhairs of Spermophora meridionalis. 



