J)ix.oi<i^N'ote on the Walking of some of the Arthropoda. 575- 



the ground before the front leg of the set. This progression of the 

 motion forwards to the anterior end of the body was also found 

 in one spider [Tegenaria Derhamii), though in this case the motion 

 on some occasions appears to commence with one of the middle 

 legs, and one photograph of another specimen showed the two 

 extreme legs moved first. In another spider [Tarantula pulve- 

 rtilenta), the house fly, and cockroach, the wave of motion started 

 in the front and travelled back along the diagonals. This wave 

 did not in any case pass continuously from one set of diagonals to 

 the other ; but there was always a much longer interval between 

 the moments of raising the first leg of one set of diagonals and the 

 putting down the last leg of the other set, than there was between 

 the moments of raising two successive legs in one set of diagonals, 

 which is the same as saying that there is a short pause between 

 the completion of the motion of each diagonal wave before com- 

 mencing the next. It is worth observing that the rule of the 

 diagonals seems also to apply to the antennae and maxillary palps 

 of the cockroach and earwig, for the antenna is twitched simul- 

 taneously with the front leg of the same side. I have not yet 

 determined how the palps of the spider move when it runs. In 

 some cases, certainly, both when moving and standing, it uses 

 them as legs ; for example, when struggling up a steep place and 

 when it comes to a sudden stop after a quick run. In this last 

 case it often raises its anterior legs aloft and waves them in the 

 air in a manner reminding one of a beetle's antennae, while it seems 

 to support the weight of the forepart of its body on its palps. 



In Phrynus renformis we find that the two anterior legs are 

 structurally modified so as to have almost completely the form of 

 antennae. Thus we may assume, as Professor Haddon has suggested 

 to me, that the legs from first being used as tactile organs (as in 

 Tegenaria) have gradually come to have the form of almost typical 

 antennae as we find them in Phrynus. In some midges, a similar 

 use is made of the first pair of legs, which, when the animal is at 

 rest, are held high in the air while it stands on the two posterior 

 pair of walking legs. Similarly when walking it barely taps the 

 ground in front of the body with the first pair of legs, while it uses 

 the remaining two pairs in the usual diagonal manner. And when 

 tapping the ground the front legs are moved according to the rule 

 of the diagonals. The aphis and several small flies exhibited besides 



