NOTES AND ADDITIONS : HOMOPTERA. 59 



to distinguish species by the mere comparison of cabinet specimens of the imago? 

 Ltew and Usten Sacken have said this of the genus (_', ridotni/in in Diptera : Osten 

 Sacken of t\vo other Dipterous genera, Sciara and re>-(itoj><xjt>ii : Norton of Tin- genus 

 Nematiis in Hynienoptera ; and Dr. Le Conte lately assured me that, although when 

 he was a young man he thought himself able to discriminate, in the closet, between 

 the different species of Brachinus in Coleoptera, he now considered it quite impracti- 

 cable to do so with any degree of certainty. And yet who doubts the fact of the 

 existence, in North America, of very numerous distinct species of Cecidomyia, of Xnara, 

 of Ceratopogon, of Xcmatus, and of Bnu-lilnus. 



Upon the same principle I strongly incline to believe that the 17-year form of the 

 Periodical Cicada (C. septemdccim, Linn.) is a distinct species from the 13-year form 

 (C. tredfeim,It\}vy) although it has been impossible for me, on the closest examina- 

 tion of very numerous specimens, to detect any speeilic difference between these two 

 forms.* It is very true that the 13-year form is confined to the more southerly regions 

 of the United States, while the 17-year form is generally, but not universally, peculiar 

 to the Northern States; whence it has been, with some show of plausibility, inferred 

 that the 13-year form is nothing but the 17-year form, accelerated in its metamorphosis 

 by the influence of a hot southern climate. But as these two forms interlock and 

 overlap each other in various localities, and as it frequently happens that particular 

 broods of the two forms corne out in the same year, we should certainly expect that, 

 if the two forms belonged to the same species, they would occasionally intercross, 

 whence would arise an intermediate variety hating a periodic time of 14, 15 or 16 

 years. As this does not appear to have taken place, but, on the contrary, there is a 

 pretty sharp dividing line between the habits of the two forms, without any inter- 

 mediate grades of any consequence, I infer that the internal organization of the two 

 forms must be distinct, although externally, when placed side by side, they are exactly 

 alike. Otherwise, what possible reason could there be for one and the same species 

 to lie underground in the larva state for nearly 17 years in one county, and in the 

 next adjoining county to lie underground in the larva state for scarcely 13 years .' 

 I presume that even 'the most bigoted believer in the old theory of species would 

 allow that, if it can once be proved to his satisfaction that two apparently identical 

 forms are always structurally distinct, whether in their external or in their internal 

 organization, they must necessarily be distinct species. 



On the other hand, I firmly believe that many perfectly distinct forms, which at 

 one time passed current, or which even now pass current, as true species, are in reality 

 mere dimorphous forms of one and the same species. We find a good example of this 

 in the dimorphous 9 Ci/nips, q. aciculata, O. S., which has already been treated of at 

 great length. We find another good example of the same thing in Cicada Cassinii $ 9 , 

 Fisher, which is sufficiently distinct from the Periodical Cicada to have been classified 

 as a distinct species, and yet never occurs except in the same year and in the same 

 locality as this last, and what is more extraordinary still, is found not only along with 

 the 17 -year form (C. septemderim), but also along with the 13-year form (C. tredecim). 



Now,' if CavHhtii were a distinct species, and not, as I believe it to be, a mere dimor- 

 phous form of C. septemdtcim and C. tredecim, the chances are more than a million 

 millions to one against its always coinciding with the two other forms, not only as to 

 the particular locality but as to the particular year of its appearance. 



1 do not know that any one has heretofore attempted to set at rest, by actual proof, 

 the very general skepticism as to this insect remaining so long undergrouud, on the 

 part of those persons who have given little attention to the subject. I have been able 

 to trace the development from year to year of my tredecim brood XVIII in the vicinity 

 of Saint Louis by digging up the larva? each year from 1868 to 1876, and noting the 

 annual growth. They could always be found within from two to five feet of the sur- 

 face upon the roots of trees, and had by the 8th year attained the first pupa stage, 

 and I have no doubt but that, at this writing, the true pupae are nearing the surface of 

 the ground to appear in myriads in the perfect state in May and June of this year. 



The fungus affecting this Cicada has since been described by Mr. C. H. Peck as Masso- 

 spora cicadina (31st Rep. N. Y. State Mus. Nat. Hist., pp. 44, 1879). 



ERIOSOMA PYRI, Fitch (Rep. I, p. 118) After comparing specimens in Europe with 

 our American insect, I have no doubt of the specific identity of the two, or of the 

 root-inhabiting and twig-inhabiting forms. The insect should be known, therefore, 

 as Schizoneura latiiyera (Hausin.). See niy remarks in American Entomologist, II, 359 ; 



* For an excellent statement of the facts bearing upon this curious question, see a paper by Mr. 

 Riley, the State Entomologist of Missouri, in Xo. 4 of the American Entomologist, and a still more 

 complete one in his First Annual Report. 



