596 PROF. E. B. POTJLTON : If A.TURAL SELECTIOIf 



(12) The Resemblances within the Limits of the Order are also 

 produced in the most Diverse Ways. 



Illogical as I believe the position to be, it is quite possible that 

 many observers may concede the force of the argument con- 

 cluded above, and yet continue to hold that the resemblances 

 w^ithin the Order are produced by external or perhaps by 

 internal causes. It can however be shown that the same con- 

 dition is true in the more restricted group as was found to 

 apply to the wider. Even within the Order itself resemblances 

 are produced in very diverse ways, although minute examination 

 is sometimes necessary before the essential diiference which 

 separates them can be revealed. 



Certain Longicorn beetles resemble weevils, the Curculionidce 

 being, so it is believed, specially defended by their extremely 

 hard chitinous covering. The weevils closely resembled by such 

 Longicorus as Doliops curculionoides and D. geometrica have 

 short antennae ending in a knob. The antennae of the Doliops 

 are nearly three times as long ; the resemblance to the weevil 

 being produced by a dilatation of the third joint, which repre- 

 sents the knob, while all the joints beyond are of such excessive 

 fineness that they are almost invisible. The strong resemblance 

 of the Longicorn Estigmenida variabilis to JEstigmena chinensis, 

 belonging to the Sispidce (Phytophaga), is brought about in a 

 similar manner, as was pointed out by C. J. Grahan. In this 

 case about one third of the length of the Longicorn's antenna 

 is concealed by its extreme fineness, while the apparent terminal 

 thickening is produced by hairs at the end of the thicker 

 section. 



In these examples, kindly shown me by Mr. Gahan, neither 

 the theory of external nor that of internal causes is of any avail. 

 It is impossible to believe that the resemblance is a direct effect 

 of climatic or other forces connected with locality, when the 

 results are in reality so utterly different and yet superficially so 

 entirely alike. The fact which requires explanation is the extra- 

 ordinary likeness in spite of the essential difference, and this, 

 when it is repeated again and again, cannot be interpreted by 

 any theory unless based upon the principle of selection. 



Many other examples of the same kind could easily be 

 brought forward : in fact, it may be admitted as a general 

 principle that in protective mimicry and common warning colours 



