May, 1902.] 



KNOWLEDGE 



99 



fall from thoir porrhes on to the ivcepUu'le awaitiui,' theui. 

 But evou tht'ii it is not oiisj to sec- them, and sometimes 

 one liuds that one has been lookinj; strai^'ht at a specimen 

 without noticing it, till it began to move, and then the eye 

 has become conscious of a sort of faint shiftint; cloud or 

 shadow, which at last resolves itself into the outlines of au 

 insect. Plotoria is therefore excellently protected. It is 

 almost invisible, at least to human vision, and even when 

 it is seen, it is found to be coloured like a bit of lichen, 

 such as mi<;ht l>e found in similar situations ; again, like 

 the re.it of the order, it has a ijland for the secretion of a 

 fluid which probablv renders it distasteful, and even if any 

 creature did essay to eat it, it would !>»> liardly wortli the 

 trouble, and would prove a very unsatisfactory morsel, as 

 there is so small an amount of matter in the hady, and the 

 hair-like lejjs and antonnie would probably get in the way. 



There are two other Briti.sh species oi this extraordinary 

 genus, both of which are much smaller insects, though 

 with e<(ually slender legs and antennie. The commoner 

 of the two is found not iinfrequently in thatch, where no 

 doubt it has a fine time amongst the immense numbers of 

 small insects of every description that delight to con- 

 gregate in such places, finding thus abundance of prey, 

 with but little trouble to itself. It is about the size and 

 somewhat of the appearance of a gnat, whence the name 

 culiei/ormis, or gnat-shaped, given to it. 



To find our next example of these stilt- walkers we must 

 go to the banks of a weedy pond, and here again good eyes 

 will be needed to detect the object of our quest, for we 

 may be looking straight at half a dozen of them and yet not 

 see them until they move. The insect we are in search of 

 is a sooty black one, called Kijihometra staynonim ( Fig. .5), 

 a representative of a third family quite distinct from 

 either of the other two, but still exhibiting the same 

 degree of slenderness in both legs and antenuor, though 

 these are not quite so long as in the other instances. 

 It will be found either parading the muddy banks under 

 the shelter of the weeds, or walking on the flat leaves 

 of the water plants as they float on the surface. It 

 is one of a very few insects that have solved tiie difficult 

 problem of walking upon the water, moving its legs in the 

 same way as when on land, and not with a skating or 

 swimmiDg movement such as is adopted by its relatives. 



FlO. 5. — Hginmetra ttagnorun 



Fig. 6. — Banalra linearis 



It moves equally fearlessly whether along the muddy 

 banks, over the Hoating leaves of the water weeds, or oil 

 the water itself, stepping from the one element to the 

 other with th.' ntninst confidence, and not even wettin" its 



feet iu the process. The practicability of this feat no 

 doubt depends upon the extreme slenderness and conse- 

 quent lightness of the insect, its weight being insufficient 

 to break through the surface tension of even so mobile a 

 liquid as water. Though capable of walking on the water, 

 it never gets far away from the water weeds, and wouM 

 probably feel itself somewhat lost if it were suddenly 

 transferred to the midst of a broad sheet of water. 



If by accident it should become immersed and so get 

 its legs wetted, it finds great difficulty in regaining its 

 position. A specimen which I once watched under these 

 circumstances tried to get out upon the leaves by thrusting 

 its legs above the water close to the edge of the leaf. But 

 each of the fine hair-like limbs, as it emerged from the 

 water, dn^w out with it a thin film of the liquid which 

 greatly hampered its movements, ami evidently needed a 

 hard struggle to get rid of. When at last it had got clear 

 and ha<l apparently escaped from the troubles of capillarity, 

 it was unable for some hours to venture on the water 

 again ; each time it attempted to do so, its minute feet 

 gradually slid outwards, and its legs, giving way beneath 

 it, left the poor creature sjirawling upon the surface in a 

 perfectly helpless condition. By refraining for some hours 

 from trusting itself to the treacherous element, it ulti- 

 mately recovered its power, and was able to walk about 

 over the water as freely as before. 



One of the strangest features in the organization of 

 this insect is the great elongation of its head, which has 

 evidently been subjected to the same lengthening influ- 

 ences as have operated upon the rest of its anatomy. It 

 projects far in front of the eyes, forming a long snout 

 which broadens at the end. There is almost an equal 

 amount of the head behind the eyes, so that the whole 

 head forms nearly one-third of the length of the insect. 

 Unlike the preceding examples, this insect is scarcely ever 

 met with in a winged condition, both pairs of wings being, 

 as a rule, aborted. 



Our last example of these stilt-walkers shall be the 

 insect called Ranatra linearis (Fig. 6), one of the so-called 

 water-scorpions, and a member of a family of Hemiptera 

 which is very distinct from all of those already mentioned. 

 One of the most noteworthy distinctions is that the 

 antennse, which hitherto have been very long, are here 

 quite minute, and are practically invisible unless specially 

 searched for, through being concealed by habitually lying 

 in a depression. This particular water scorpion is not a 

 very common species, and as it lives at the bottom of 

 weedy ponds, only occasionally coming to the surface, it is 

 scarcely ever seen unless caught in a net, or secured by 

 dragging the weeds out of the pond. It is a large insect, 

 far exceeding the dimensions of our other examples, and 

 therefore, of course, its legs, though still very slender for 

 a creature of such size, are not absolutely so thin as in the 

 previous instances. They are, however, sufficiently stilt- 

 like, both in shape and in use, to warrant our including 

 their possessor amongst the subjects of this pjaper. These 

 thin legs, of course, offer very little resistance to the water 

 as liaiiiitra moves about at the bottom of its pond, or 

 amongst the water-weeds. Anyone who is accustomed to 

 sea-bathing, and knows by experience how laborious a 

 process the human being with his thick legs finds it to 

 make his way on foot through the water, will appreciate 

 the advantage conferred upon Banalra by its spindle- 

 shanks, and hence we see a distinct line along which 

 natural selection may have proceeded in producing so 

 extrat)rdinary an insect. From the figure it will be 

 observed that only two of the three jjairs of legs have been 

 modified in this jiarticular way. The front pair have 

 reached a degree of specialization which is even more 

 remarkable. Here the tendencv to elongation has been 



