POPULAR SCIENCE 247 



regular surface, so that their motion could be carefully watched. 

 It was thus rendered evident that — 



1. The longest legs, those of the first and fourth pairs, 

 move along the lines of their own directions by vertical bending 

 of the joints ; the shorter legs of the second and third pairs 

 move forward by rotation from the coxae, at right angles to 

 their own directions. 



2. First near leg moves with the fourth off leg. (a) 

 Second ,, „ ,, „ „ third ,, (b) 

 Third ,, ,, ,, „ ,, second ,, (c) 

 Fourth „ „ „ „ ,, first „ (d) 



3. Walking consists of (a) and (c) simultaneously, followed 

 by (b) and (d) simultaneously. 



During this investigation it became quite clear that the 

 spiders that were tiring themselves on the water were most 

 certainly swimming. A spider dropped on the surface of 

 a sheet of water does not sink. From below, total reflection 

 shows that a film of air lies between its ventral surface and 

 that of the liquid, while so long as the creature remains still 

 the legs indent the surface but do not pierce the " skin " caused 

 by capillarity. Motion, when induced, begins with extreme 

 rapidity, but after half a minute slackens and proceeds in pre- 

 cisely the same manner as in walking. 



The first and fourth pairs of legs slide over the surface, the 

 latter lying flat thereon for the last two joints. It would seem 

 that they have little if any propulsive effect. The second pair 

 penetrates the surface about two joints deep, the third pair 

 one joint. I think that nearly all the propulsive effort is afforded 

 by these pairs. It is manifest that these Tegenaria were indeed 

 swimming, and not, like Lycosidse, Pisauridae, etc., running 

 on the water. For, in these latter cases, the first and fourth 

 pairs of legs are not slipping ; the second and third pairs are not 

 thrust into the water ; and the body is supported on the legs 

 in the ordinary way and not resting on the water. Again, 

 though entirely distinct from the subaqueous activities of the 

 water spider, it resembles them in that free and not dissolved 

 oxygen is provided. 



Finally, the spiders that had swum and walked at my 

 command were returned to their cages and one and all 

 settled down at once to what was, perhaps, the most interesting 

 series of actions of all. They proceeded to complete their 



