Februaky 1, 1892.] 



KNOWLEDGE 



20 



effort and fussy energ}-, imparted to it, simply by varying 

 its position and by altering the attitude and motion of the 

 jaws and antenn*. 



Hitherto, we have been speaking only of the wingless 

 forms of Ants, but these, though by far the most 

 numerous, by no means constitute the whole of any given 

 species. Every Ant exists in three forms, the male, the 

 female, and the worker. Both the male and the female always 

 have wings when first they assume the perfect form ; the 

 latter sex, however, retain them only till the marriage 

 flight is over : they then voluntarily tear them off, so 

 that in this sex the wings are only temporary appendages. 

 These winged forms are seen for so short a time during 

 any single season, that many people no doubt have 

 never noticed them at all, and find it difficult to believe 

 that such things exist. But even when one does see them, 

 which will probably take place some fine day m August or 

 September, it is often difficult to recognise them as having 

 any connection with the wingless workers with which one 

 is so familiar. It is clear that if two pairs of membranous 

 wings, one large, the other small, be supposed to be added 

 to a worker Ant, such an addition would of itself greatly 

 alter the appearance of the insect. But this is by no 

 means the only difference ; there is also often a striking 

 dissimilarity both with regard to size and colour, and the 

 males, which are the smaller of the two, are frequently 

 also much unlike their partners in colour and shape. For 

 example, the little yellow Ant ( Lad us tiatm), which is 

 abundant in many meadows and on heaths, making little 

 hillocks, or taking advantage of the protection of a large 

 stone or loose piece of rock, is yellow only in the worker ; 

 the male and female are both brownish black ; or again, 

 the little thin red Ant (Mijrmka nihni), which is common 

 everywhere, has a dark blackish brown male, which, in 

 consequence of its wings and its deep colour, would be 

 supposed to be a totally different insect from the worker. 

 or the female. It is, then, only the workers that have no 

 wmgs, or the females after they have mated, but then in 

 this latter case the stumps of the wings may still be seen, 

 whereas iu the workers two little rounded points alone 

 represent that portion of the larval structure which iu the 

 males and females developes into wings. 



The development of wings iu the male and female Ants 

 has an important influence on the shape of the thorax, 

 which adds another means of distinguishing the latter from 

 workers when they haVe lost their wings. In the workers, 

 the three segments of the thorax are not very unequal in 

 size (Fig. 2 1, as each contains similar sets of muscles, viz., 

 those for one pair of legs only ; but when the wings are 

 developed additional muscles are needed for these, and 

 must be accommodated m the two hinder segments ; hence 

 the prothorax (first segment) becomes overlapped by the 

 greatly enlarged mesothorax (second segment), which gives 

 a still more humpbacked form to the insect, and the meta- 

 thorax also (third segment) becomes enlarged. The 

 enlargement is greatest in the mesothorax, as that segment 

 has to carry the first pair of wings, which is by far the 

 larger of the two, and is the chief instrument of flight. 

 The wings are composed of transparent membrane, more or 

 less clouded with a smoky tint, and strengthened by a few 

 nervures, which enclose only a small number of cells. 



Now the other wingless Hymenoptera with which Ants are 

 often confounded do not exist in these three forms ; all 

 examples met with will be either males or females, no 

 such things as workers being known, for a very good 

 reason, viz. : — that there is no work for them to do. The 

 insects do not form communities, but are, as already 

 mentioned, piratical in habits, each managing its own 

 affairs, which, in the case of the female, consist of little 



more than finding a suitable host in whose body she may 

 deposit her eggs. These insects do not, as the Ants, 

 couple iu the air, and therefore never have any wings at 

 all. It will be impossible, then, ever to fiud such insects 

 in communities, or winged, in both of which respects they 

 are to be distinguished from Ants. It should be observed, 

 however, that some species, of which the females are 

 always wingless, have winged males. 



We are now iu a position to answer our query " What 

 is an Ant ? " We have seen that Ants are Hymenopterous 

 insects, which live in communities comprising three types 

 of individuals, males, females, and workers ; that the two 

 former ones are winged and are to be met with only 

 at a certain season in the year, but that the latter 

 are never winged ; that the antennas are elbowed, and that 

 the abdomen is attached to the thorax by a knotted petiole. 

 And as they possess a poison gland and either a rudi- 

 mentary or fully developed sting, they are referred to that 

 section of the order called the ■' Aculeate " (sting bearing) 

 Hymenoptera, which also contains bees, wasps, and some 

 other insects. Lastly, they constitute a compact group of 

 this section, to which the name HeterogjTia has been 

 given, iu consequence of the great size and very different 

 appearance of the females {(inrk : dissimilar females). 



THE CANONS OF COLORADO. 



[Second I'dpcr.J 



By the Eev. H. N. Hutchjxsox, B.A., F.G.S. 



{ContiniU'd from pnrje 11). 



CEETAIX important consequences foUow from the 

 rules about rivers, laid down at the end of our last 

 paper. Thus, when rivers flow through or across 

 mountain chains and plateaus, they must be older 

 than these structural features. The elevation of a 

 platform across the track of a river rarely diverts it fi-om 

 its com'se, because as fast as the ground under the river 

 rises it cuts its way down through the obstruction. The 

 region we are now considering offers a very complete 

 illustration of the rules pre\iously stated. We know 

 that during the whole of Mesozoic time the watershed 

 of the Colorado was submerged. In early Cainozoic 

 (Lower Eocene) time it was a great freshwater lake. In 

 due time this lake was drained, or emptied, presumably by 

 the cutting down of its outlet as the country rose. By 

 this process the present drainage system was begun, and 

 every river must then have run in conformity with the 

 features of the surface just exposed after rising above the 

 waters of the lake, in which the Lower Eocene rocks were 

 formed. But to-day we find that surface greatly deformed 

 by displacements, and by erosion. The former made the 

 " faults ' and monoclinal flexures ; the latter carved 

 teiTaces out of the Eocene strata. The present courses 

 of the rivers are not what they would have been if 

 these features had then been in existence. They are 

 entirely independent of them. They run iu most cases 

 against the slopes, and against the inclinations of the 

 strata. They even cut through mountains and plateaus, 

 enter cliff's and emerge fi'om them ; they flow over the 

 monoclinal folds ; they cross " faults " from the upthrow 

 to the downthrow sides. As before stated, these facts can 

 only be explained on the assumption that the rivers are 

 older than the changes represented by all these structural 

 features. 



Many complex operations are involved in the evolution 

 of the Grand Cauon, but the main factor is the erosion of 

 its platform, and all the others are found to be bound up 



