52 THE GENESIS OF SPECIES. [CHAP. 



undergoes a sort of liquefaction of a great part of its body, 

 while certain patches of formative tissue, which are attached 

 to the ramifying air- tubes, or tracheae (and which patches 

 bear the name of " imaginal disks "), give rise to the legs, 

 wings, eyes, &c., respectively ; and these severally formed 

 parts grow together, and build up the head and body by 

 their mutual approximation. Such a process is unknown 

 outside the class of insects, and inside that class it is only 

 known in a few of the two-winged flies. Now, how 

 " Natural Selection," or any " laws of correlation," can 

 account for the gradual development of such an exceptional 

 process of development so extremely divergent from that 

 of other insects seems nothing less than inconceivable. 

 Mr. Darwin himself l gives an account of a very peculiar 

 and abnormal mode of development of a certain beetle, the 

 sitaris, as described by M. Fabre. This insect, instead of 

 at first appearing in its grub stage, and then, after a time, 

 putting on the adult form, is at first active, and furnished 

 with six legs, two long antennae, and four eyes. Hatched 

 in the nests of bees, it at first attaches itself to one of the 

 males, and then crawls, when the opportunity offers, upon 

 a female bee. When the female bee lays her eggs, the 

 young sitaris springs upon them and devours them. Then, 

 losing its eyes, legs, and antennae, and becoming rudimen- 

 tary, it sinks into an ordinary grub-like form, and feeds 

 on honey, ultimately undergoing another transformation, re- 

 acquiring its legs, &c., and emerging a perfect beetle ! That 

 such a process should have arisen by the accumulation of 

 minute accidental variations in structure and habit, appears 

 to many minds, quite competent to form an opinion on the 

 subject, absolutely incredible. 



1 "Origin of Species," 5th edit, p. 532. 



