112 Miscellaneous, 



the abnormal specimen the left superior wing has only three mar- 

 ginal cellules instead of four, the most basal being absent. The 

 monstrosity was thus of the same nature and affected the same side 

 as in our G. pedicalarius *. 



The right wing of our teratological example possesses, indeed, the 

 second posterior marginal cellule, but it is abnormal from another 

 point of view. While in the normal condition the branch of the 

 radial nervure and the median nervure are united over a certain 

 extent of their course (figs. 1 and 3, A), in the abnormal wing these 

 two nervures touch at a single point (fig. 2, A), thus realizing a 

 condition which we find normally in certain Psocids, notably in the 

 genus Mesopsocus, Kolbe. 



De Selys Longchamps has already pointed out that a similar 

 character would be insufficient to separate Mesopsocus from Elip- 

 socus; certain examples of Elipsocus unipunclatus, Mull., present, 

 in fact, a disposition of the nervures which is intermediate between 

 the type of this species and Elipsocus laticeps, Kolbe f. 



The teratological variations in the reticulation of the wings of 

 insects appear to bo abrupt and in discontinuity with the normal 

 condition. If they are preserved by heredity they constitute new 

 varieties, sometimes even new genera or species if other characters 

 are modified in addition, so as to allow of a more complete differ- 

 ential diagnosis. Starting from this point, certain naturalists have 

 maintained that all species have a similar origin, and that the action 

 of the primary or secondary factors of evolution, Lamarkism and 

 Darwinism, should give place to this new conception of the descent 

 of living beings by discontinuous teratological modifications. 



This, we think, is an inexact and exaggerated interpretation of 

 facts which in themselves are highly important. The production 

 of species by a discontinuous process remains a particular case whose 

 importance may have been undervalued, but on which it is not 

 advisable to found a general law. 



In reality the different types of neuration represent so many 

 stable states of equilibrium between which no continuous gradual 

 passages can be established. The forms intermediate to these states 

 of equilibrium are not realized, because they do not correspond to 

 conditions of sufficient stability. To make use of a trivial com- 

 parison, one cannot show the half or any fraction whatever of one step 

 of the ladder. In similar cases the progress is very discon- 

 tinuous or, what comes to the same thing, only manifests itself in a 

 discontinuous manner. But we cannot derive from these facts any 

 argument against the formation of species by natural selection, still 

 less can we find there the sole and complete solution of the com- 

 plex problems of metamorphism. — Actes de la Sociele Scientifique 

 de Chili, t. v. 1895, l re livraison, pp. 19-21. (Communicated by 

 the Author.) 



March 8, 1895. 



* De Selys Longchamps, "Revision des Psocides decrites par Rambur/' 

 Ann. Soc. Entomol. de Belgique, t. xvi. p. 6 (1873). 



t "Catalogue raisonne des Orthopteres et des Nevropteres de Bel- 

 gique," Ann. Soc. Entomol. de Belgique, t. xxxii. p. 128 (^1888). 



