Page:Phylogeny of cynipid genera and biological characteristics.pdf/14

 simplicity, of Disholcaspis of one degree and sort of complexity, of Amphibolips of another, etc. The absolute uniformity in these genera of the degree of complexity needs to be fully realized, for it has some significance. In several genera, Rhodites, Neuroterus, etc., there is a range, more or less wide, in the degree of complexity of the galls of a single genus and, with our present inadequate knowledge, we cannot be sure what this may mean; but such instances do not invalidate the force of the fact that in many cases the degree of complexity of gall structure is a definite indicator of the generic nature of the insect.

If the gall (however it may be produced) is an expression of the physiological make-up of the insect; if the form of the gall is an expression of both the specific and generic constitution of the insect; if the degree of complexity of the gall is a definite guide to the generic nature of the insect; then we may believe that the degree of complexity of gall structure is an expression of the degree of development, evolutionarily, of the insect. Specific and generic characters are merely expressions of the relationships of the origin, in the course of evolution, of the organism, and anything which is constantly an expression of these generic qualities (as the gall structure and degree of complexity undoubtedly are) will indicate these evolutionary relationships. This is my justification for believing that the simplest galls are found among the most primitive Cynipidæ, and that the most complex galls are found only among the highest Cynipidaæ We must admit that there seems to be nothing known that demands that only the highest cynipids produce complex galls, but this ignorance is due, patently, to the fact that we know nothing of the way in which galls are produced. All we can say is that some activity on the part of the insect is responsible for the gall production, and it is in no wise unreasonable to think of that activity becoming more potent in its effect as the insect has evolved.

In the accompanying table of the gall characters of certain groups of Cynipidæ the genera have been arranged in the order of an increasing degree of complexity of the gall, and we believe that order to be in some degree the order of origin of the genera, making due allowances for the inadequacies of a linear arrangement of an evolutionary series. We may allow details of relationships to be worked out by other lines of evidence, but we should attach some importance to the very primitive character of all the galls of Aulacidea (without a single exception), to the less primitive but still simple qualities of the galls of Aylax, Diastrophus, and Neuroterus, and to the highly developed characters of the galls of Cynips (European sense), of Disholcaspis, and of Amphibolips.