MIMICRY. 299 



which both upper and lower wings have become elongated in an 

 approach to due proportion."* This complicated classification, 

 which expresses the difficulties and intricacies of evolution in 

 every sentence, naturally sometimes fails in the details of its own 

 arrangement, but is sufficient to throw more than grave doubts 

 on the explanation offered by Prof. Semper. The consideration 

 of the present knowledge applicable to these Phasmidce appears 

 to warrant the following conclusions : — 



1. The Walking-stick insects are usually considered by natur- 

 alists to be undoubted examples of " Protective Resemblance," 

 due to a process of " Natural Selection." 



2. If they are found with a somewhat similar structure in 

 the Carboniferous fauna, they must therefore be the result of a 

 previous course of evolution. f 



3. Reptiles and birds, well-known insect enemies, are gener- 

 ally considered as posterior to the Carboniferous epoch. 



4. But as the Permian reptiles were fully developed as we 

 know them now, they must have had an earlier and less differ- 

 entiated structure ; the same suggestion being applicable to the 

 Jurassic birds. 



5. The presence of the imitative Phasmidce in the Carboni- 

 ferous epoch implies the existence of enemies, probably reptiles, 

 and possibly a transitional form of bird-life. 



Good cause is shown why we should seek in past geological 

 epochs for the earliest traces of protective resemblances and 

 mimicry, for the absence of observed attack in the present time 

 does not disprove a great danger and want of protection in the 

 dim eras of the past. " In studying protective resemblance and 

 mimicry among living animals, the exceedingly common occur- 

 rence of these phenomena has often forced upon me the con- 



* " Descriptions of Fifty-two New Species of Phasmidce'" (Trans. Linn. 

 Soc. vol. xxv. p. 323). 



f Our knowledge of pre-Carboniferous insects is limited, but present 

 knowledge goes to prove that a considerable insect-fauna existed in more 

 ancient times. Thus, as Mr. Comstock has observed: — "Of Devonian 

 insects we know several. . . . These differ among themselves to such an 

 extent that we are forced to conclude, without taking into account the two 

 known Silurian insects, that already at that early time there was a large and 

 varied insect-fauna, of which the more primitive forms have not been dis- 

 covered" ('Evolution and Taxonomy — The Wilder Quarter-Century Book,' 

 p. 55). 



