152 



CALIFORNIA ACADEMY OF SCIENCES. 



Fig. 3. 



always either approaching each other or are receding 

 from each other. 



The prothoracic legs do 

 not move synchronously 

 with either of the other 

 pairs nor with each other. 

 Generally ( fig. 3 ) one 

 moves backwards while 

 the other is reaching for- 

 ward. They appear mainly 

 to guide the body. The 

 femoro-tibial joint is most 

 of the time in front of the 

 tarsal claws, so that their 

 power as propellers cannot 

 be great. The parasite 

 thus progresses along the 



feather with a hand over hand movement of the pro- 

 thoracic legs, as of a man climbing a rope, while the 

 other legs, a pair at a time, are continually pushing the 

 body forward. 



This is the typical movement of the legs and the one 

 which prevails when the insects are walking quietly 

 and regularly, but at times it becomes very much 

 obscured by irregular movements and is generally more 

 or less so, so that almost any relative position of the 

 legs may be seen. The outer end of the metathoracic 

 femur is seldom brought much farther forward than 

 its coxa. The mesothoracic femur forms a smaller 

 angle with the body in front, but not such a small 

 one behind as the metathoracic leg. The femoro-tibial 

 joints of the prothoracic legs are during progression 

 brought forward, and the tibia also independently turns 

 forward on the femur, so that the angle between the 

 two increases and the tarsal claws are carried forward 



