—59— 



in abundance in Louisiana, was at that time very constant, every spe- 

 cimen (of forty-three collected) being- marked exactly the same, the 

 normal form being represented (see Psyche, vol. IV, p. 222). But Prof. 

 Riley has described and figured many variations of it from the West, 

 which were doubtless taken when the species was in its normal state of 

 abundance. Eight specimens of lapponica Linn, taken here (where I 

 have never known it to be abundant) show a series of five well marked 

 variations. 



The cause of the constancy of a form when it becomes very numer- 

 ous in individuals is at first somewhat hard to see. We would naturally 

 suppose that under such circumstances it would be very inconstant, as 

 sexual selection would seem to have played no part, but all the indivi- 

 duals would naturally have had to pair to produce such abundance. But 

 here is just where we overlook the part which sexual selection has played 

 — and it certainly is the cause to which this constancy is to be attributed. 

 The form of a species which first begins to multiply rapidly and thus gets 

 ahead of its kindred forms (it is likely to be the typical form, as that is 

 the most numerous in individuals), is the one that will win. And it will 

 be constant because sexual selection preserves the standard of beauty in 

 a race which standard is determined by the majority. Now the large 

 majority in a species that has begun to increase is the typical form, and 

 from this we see that if a species happens to multiply unduly (we know 

 not from what cause) and thus gets a start, it will perpetuate its type and 

 remain constant, while its kindred variations will be pushed to the wall 

 in the struggle lor existence. Some influence seems to guard the pro- 

 pagation of a form while it is in a state of abundance, so that only the 

 form itself is produced and no variations occur. The image of the favor- 

 ed form, so predominant and numerous, seems to be deeply fixed in the 

 being of the parent-beetle to produce this form. But as long as the 

 species is in its accustomed state, variations are very frequently produced; 

 and moreover they find room for themselves and increase. At all events 

 these are the facts; I have given the explanation as I see it. 



In conclusion, if C. scalaris Lee. is shown, as it no doubt will be, 

 to graduate by variations into the form of philadelphica Linn., it will have 

 to be considered a variety of the latter; though other forms, as nearly 

 related as these two, but not having connecting variations, must neces- 

 sarily be regarded as distinct species. In other words scalaris is not a 

 perfected species yet, but will be in time. How long a time may be 

 told by entomologists some centuries hence, when its connecting varia- 

 tions have passed away or developed into new species. 



