24G 



KNOWLEDGE. 



[November 1, 1894. 



illustration of the law of correlation of structures, of which 

 many others may be observed in the same two insects. 

 Consider, for example, the following details of symmetry 

 and contrast : in the vigorous and active bluebottle we 

 find a stout, heavy body, short legs, short, strong wings 

 with large alulas, a short compact head, insignificant 

 balancers, and a body beset with stout bristles. In the 

 fragile and weakly crane-fly all these points are reversed, 

 and we find a long, slender, light body, very long legs, 

 long narrow wings without alulfe, a long and tapering 

 head, large and conspicuous balancers, and a smooth and 

 bristleless body. 



The shape of the thorax, strongly convex and hump- 

 backed above, is worthy of notice, as representing in an 

 almost exaggerated degree the general plan of dipterous 

 structure in that part of the body. Eemembering that 

 each of the three pairs of legs represents a separate division 

 or segment of the thorax, it will be comparatively easy to 

 trace the limits of these regions, by following the junctions 

 upwards from the points of attachment of the legs. It will 

 thus be seen that the prothorax, or first region, is reduced 

 to very small dimensions, forming no more than a sort of 

 collar, just behind the head. The metathorax, or third 

 division, a much larger mass, wUl be found behind ; but 

 when we have marked off these two parts, there still 

 remains the greater ijortion of the thoracic mass, which is 

 thus proved to belong to the second segment, or mesothorax. 

 If we bear in mind that this is the division which, in 

 insects generally, carries the fore wings, and that in flies 

 the fore wings are the only pair developed, the reason for 

 the great development of this part will be at once evident, 

 for within its cavity are stored the muscles that are instru- 

 mental in working the wings. There is one feature of the 

 mesothorax that is specially characteristic of the family 

 we are now considering, a trivial feature no doubt, but one 

 which is helpful in distinguishing Tiindida- from other 

 groups. Across the middle of the upper surface runs 

 a \'-shaped furrow, which is not to be found in other groups 

 of flies, for the rest of the order either have a smooth 

 surface here, or if a transverse impression is present, it is 

 incomplete and not V-shaped. At each side of the thorax 

 will be seen two narrow slits, one just above and behind 

 the insertion of the first pair of legs, and the other at the 

 base of the balancers. These are two of the spiracles, or 

 entrances to the breathing tubes, which, as with insects 

 generally, traverse all parts of the body and convey air to 

 the system at large. 



The head (Fig. 1) is most peculiar in shape, being pro- 

 longed into a sort of beak. The basal part is almost 

 globular, and the compound eyes 

 occupy a large part of the surface 

 here. In life they are of a bright 

 green colour, a very pleasing relief 

 to the sombre tints of the rest of 

 the body ; unfortunately, however, 

 the colour is fleeting, and passes 

 away after death. At the end of 

 the beak are two jointed organs, 

 which, when not in use, are carried 

 bent back underneath the head ; 

 these are the maxillary palpi. The 

 upper part of the head carries the antennre, a pair of 

 long, jointed, tapering organs, with circles of delicate 

 bristles at the junctions of the joints. The form of the 

 antennno decides at once to which of the two great divisions 

 of flies the crane-fly belongs, viz., the Nemocera, or 

 " thread horns." This, again, is another respect in which 

 it difl'ers markedly from the bluebottle and other flies of 

 that robust type, which have short and most oddly-shaped 



Fia.l.-Uead of Daddy, 

 longlcgs. 



Fio. 2.— 

 Ovij^ositor 

 of I) a d d y- 



loiifrU'gs. 



antennre. It is hardly necessary to say that no biting 

 jaws exist in the perfect insect. No power of biting or 

 piercing is possessed by it, and hence its harmlessness in 

 this stage, whether to man, beast or plant. 



The legs, as already mentioned, are exceedingly long 

 and slender, each of the divisions being elongated to a 

 considerable extent ; the tarsi, or feet, which are five- 

 jointed, with the joints diminishing in length as tbey 

 recede from the body, are even longer than the tibise. 

 They are not only long and slender, but also very fragile 

 and easily broken off, an accident to which 

 the insects are extremely liable, but at the 

 same time one which cannot be regarded as 

 of a serious character, for the loss of even 

 half the number of its legs does not prevent 

 the insect from going about its business as 

 though nothing had happened. Such losses 

 can hardly be attended with much pain, and 

 their chief influence would no doubt be felt 

 in the difliculties in steering during flight, 

 which would follow. Unlike crabs and 

 lobsters, the daddy-longlegs does not possess 

 the power of reproducing a lost limb, nor 

 indeed would the power be of any avail if 

 it existed, since the insect's adult life is 

 too short to allow time for any such restored limb to 

 grow. 



The hinder part of the body difi'ers markedly in the two 

 sexes. In the male it is blunt and swollen, the enlarged 

 part containing a complex reproductive apparatus ; but in 

 the female, it tapers regularly to a hard and sharp point. 

 This acute tip (Fig. 2) is the hardest part of the body, and 

 necessarily so, as it has to do the hardest work, and indeed 

 the only serious work that devolves upon the fully-matured 

 insect. It constitutes an egg-laying instrument of superior 

 quality, and is composed of four pieces disposed in pairs. 

 On the upper side are two long and pointed pieces which 

 form the sharp tip, and are used as borers, and underneath 

 these is the other pair, considerably shorter, broader, and 

 blunter, their function being to guide the eggs in their 

 passage into the hole prepared for them by the pair of 

 borers. The whole apparatus, therefore, is something like 

 a combination of an auger and a spoon. 



The eggs are small, shining black, and slightly curved. 

 When they are about to be laid, the mother insect behaves 

 in a most remarkable manner — in a manner, indeed, that 

 might have been thought impossible had it not been 

 actually witnessed. It will be remembered that in those 

 animals in which a distinct longitudinal axis of the body 

 can be traced — such, for example, as vertebrates and 

 arthropods — -the almost universal position of that axis is 

 horizontal, the chief exceptions being man and birds, whose 

 use of only one pair of limbs in walking throws their axis 

 into an erect or sloping position. So in insects and other 

 arthropods, as the bipedal arrangement does not exist, one 

 naturally expects to find the axis of the body placed 

 horizontally when the animal is walking over a level 

 surface, and in fact it is a most exceptional circumstance 

 that any other disposition should occur. When, therefore, 

 it turns out that the female daddy-longlegs, on its egg- 

 laying expedition, actually struts about on its hind legs 

 with its body placed in a perfectly erect position (Fig. H), 

 it will be admitted that we are justified in considering 

 this most extraordinary behaviour. Considering the struc- 

 ture of the legs, however, it is evident that the proper 

 balancing of the creature, if it had to depend on its hind 

 legs only, would be a somewhat nice operation, and hence 

 the pointed abdomen is requisitioned as an auxiliary, and 

 is used as a third prop. Most ludicrous is the sight as 



