576 Scientific Proceedings, Uoyal Dublin Society. 



the diagonal walk several irregular walks, sometimes moving all 

 the legs on one side, beginning with the first or third before moving 

 those of the other side. 



The diagonal walk, Mr. Muybridge has shown to apply, with 

 but a single exception, to all mammalia ; it is observable too in 

 newts, lizards, and tortoises, and, as stated above, it is the general 

 rule in the case of the Arachnida and Insecta. It does not, how- 

 ever, appear to hold universally ; thus in the case of the single 

 representative of the group Thi/sanura {Tomocerus longicornus] 

 which I have examined, the opposite legs are often moved simul- 

 taneously, in pairs, especially when the sucker placed on the abdo- 

 men is brought into play. This mode of locomotion is also found 

 as the rule in caterpillars, and less often in a coleopterous larva 

 which I have observed. It is peculiarly interesting that these larval 

 forms present the same method of progression as the Thysanura, 

 which are regarded as having preserved most completely the primi- 

 tive character of the oldest insects. 



In the caterpillars the wave begins with the two most posterior 

 false legs and proceeds forwards. This wave when it reaches the 

 middle of the body gives rise to the characteristic attitude of the 

 " Loopers." 



Besides the photographs looking vertically down on the 

 animals, I have also taken a few side views or profiles, which, 

 though not so useful for making out the walk, show some interest- 

 ing attitudes, e. g. when lifting the back legs the spider first raises 

 the most distal part of the leg which touches the ground and then 

 the more proximal part ; and similarly in putting down the legs it 

 is the extremity of the leg which reaches the ground first. 



Often, when the Tarantula was put on the floating paper, after 

 some hesitation it took to the water, and succeeded admirably in 

 making way on its surface. When in this position, the tips of its 

 legs, and sometimes its palps and lower surface of abdomen, made 

 capillary depressions in the surface of the water. These conical 

 depressions converted the water into a diffusing lens, and conse- 

 quently produced a dark spot on the bottom of the dish, surrounded 

 with a bright ring, which corresponded in size to the depressions 

 on the surface. As the diameter of the depressions depends 

 upon the weight on the point which causes them, and as the 

 shadows are a measure of the depressions, it follows that the ratio 



