THE WEAK SIDES OF NATUKAL SELECTION. 65 



assume the form of maturity. But in one of the most primi- 

 tive groups, the Orthoptera, there are no such changes. The 

 young cockroach issues from the egg not as a grub or a 

 maggot, but a miniature of the adult insect, from which, 

 indeed, it differs mainly by the absence of wings. But the 

 Orthoptera, and in particular the cockroach group, seem to be 

 among the most ancient forms of insects — indeed, according 

 to some authorities the most ancient of all true insects. It 

 is further supposed that all insects are ultimately descended 

 from the Thysanura. These creatures also do not undergo 

 a metamorphosis. Thus there arises the question how, on 

 the principle of Natural Selection, the metamorphotic charac- 

 ter in the higher and more recent orders of insects can have 

 arisen ? Where has been the advantage, or in other words, 

 how has this change contributed to the preservation and 

 multiplication of the species ? We all know that the cater- 

 pillar, the grub, or the maggot is more helpless than the 

 insect in its mature form. Its organs of sensation are less 

 developed and its locomotory apparatus is less efficient. We 

 are then almost forced to conclude that insects cannot have 

 become metamorphotic by a process of Natural Selection. 



Another difficulty is the disappearance of the hind-wings in 

 the Diptera, such as the gnat, the house-fly and their kindred. 

 We find the other orders, both earlier and more recent, pro- 

 vided with the normal four wings, and we do not readily see 

 how, on the principle of Natural Selection, the Diptera should 

 have lost the hinder pair. 



Among the vertebrate animals we find similar questions 

 suggested. We take the fore-leg of the lizard and the wing 

 of the bird, and we find each of these limbs useful. But if 

 Natural Selection has gradually modified the one into the 

 other it is hard to conceive how the earliest steps towards 

 developing the leg into the wing could have been of the 

 slightest use to the creature in question. And unless useful, 

 such variations should not, on Darwin's hypothesis, havebeen 

 reproduced and continued. 



Perhaps the most decisive case of the inability of Natural 

 Selection to account for some particular structure is the 

 position of the mouth of the shark. EA T eryone knows that 

 in fishes or reptiles generally the mouth opens at or very near 

 to the foremost extremity of the body. Take up a herring, 

 a frog, a serpent, or a lizard and imagine how strangely the 

 animal would be inconvenienced in attempting to seize its 

 food, and at what a disadvantage it would be placed in 



