200 [November 



alone; much in the same way as Conchologists used formerly to neglect 

 and undervalue all the soft parts of a Mollusk, and decide on its syste- 

 matic affinities only from the characters of its shell. 



But although it is difficult to assign any good reason for making the 

 imago the sole criterion of specific identity, it maybe readily understood 

 how the practice originated. The imago is easily preserved so as to 

 retain its characters unimpaired ; the larva is preserved with difficulty, 

 and frequently cannot be preserved at all without losing its shape and 

 its color. The imago may be collected vicariously, and studied in the 

 closet a thousand miles from its habitat ; in order to study the larva, 

 the naturalist must, in many cases, go forth personally into the woods 

 and the fields, and contemplate the living animal on the very spot of 

 ground where, and at the very time of year when, it is to be met with. 

 Hence the imago with many systematists has become everything, the 

 larva and pupa nothing. But if it so happened that larvae were easily 

 preserved in cabinets, and imagos with 'difficulty, then it is not impro- 

 bable that closet-naturalists would neglect and undervalue the charac- 

 ters of the imago, just as many of them now neglect and undervalue 

 those of the larva. Genera and species would then be characterized 

 almost exclusively from the consideration of the larva, just as they now 

 are characterized almost exclusively from the consideration of the imago; 

 and entomologists would be no more disconcerted at findino; two dis- 

 tiuct species undistinguishable in the imago, than they now are at find- 

 ing two distinct species undistinguishable in the lai'va state. 



On the general principle that, whenever two insects diifar by con- 

 stant and well-marked characters in any of their states, whether egg, 

 larva, pupa or imago, they must be specifically distinct, unless they be 

 the sexes or other dimorphous forms of one and the same species, the 

 case of tessellaris and Harrisii might be rested here. But there is ad- 

 ditional evidence of their specific distinctness. The former occurs upon 

 a great variety of trees — oak, basswuod, elm, hackberry, hickory, thorn, 

 soft maple, and, according to Abbot, on beech, hornbeam, and plum — 

 but never, as I have this year carefully noticed, upon sycamore, (pla- 

 tanus;) the latter occurs exclusively upon sycamore. At first sight we 

 might account for these facts, upon the hypothesis that the colorational 

 peculiarities of Harrisii are due to its feeding upon sycamore; and that 

 if a young tes^clhtris were fed upon sycamore, it would gradually, as it 

 approached maturity, pass into Harrisii ; in other words, that the two 

 so-called species are mere Phytophagic Varieties. But experiment de- 

 monstrates the fallaciousness of this supposition. I have this year sue- 



