Page:Phylogeny of cynipid genera and biological characteristics.pdf/3

 It may be considered that the open radial cell is more highly specialized than the closed cell, for the process.of openiiAg in this instance involves the disappearance of the marginal vein and later of the extremities of the subcostal and radial veins. It would be surprising to find that species with the open radial cell had developed the veins necessary to close the cell and thus originated the closed-cell forms. Evidence of evolution based on a consideration of this point alone would be meager enough, but if it parallels the data of other sorts it will lend that much more weight to the final conclusions, and at a couple of points it will bridge gaps in the history.

From the table it will be seen that the character of the radial cell is of generic importance. Although it is true that Aulacidea is separated from Aylax primarily upon this character and that this is the best reason for considering Aulacidea a distinct group from and more primitive than Aylax, nevertheless, in many other instances where the genera are founded upon other morphological characters, it will be seen that the condition of the radial cell is as good a generic character. Thus, for instance, Disholcaspis is a genus founded on peculiarities of thoracic sculpture, the size and shape of the second abdominal plate, and the shape and proportions of parts of the head, among other very definite characteristics. The occurrence of the open radial cell in all the known species of that genus suggests that the genus as a unit is descended, rather indirectly, from a group with the closed cell. On the other hand, in Rhodites, a genus maintained likewise on abundant, definite morphological and biological characters, although thirty of the species have the cell entirely closed, six species have the cell more or less open. It seems probable that in this instance the group has originated directly from a closed-cell genus, and that comparatively recent evolution within Rhodites itself has given rise to the few species which possess the open cell.

The order in the accompanying table is that of the apparent order of evolution, as indicated by this sort of evidence only. Again, I acknowledge the meager value of these considerations, except they be judged in connection with the other sorts of data present in this paper.