BY R. J. TILLYARD. 283 



postpone the definition of Archetypes until the whole of the 

 characters selected have been surveyed; and the final decision 

 as to the phylogenetic relationships of the various Orders will 

 not become fully apparent until the work is completed. Mean- 

 while, it seems advisable to select the characters for study in 

 such a way that the work can be subdivided up into a series of 

 parts, each complete in itself, and suitable for separate publica- 

 tion. Working on these lines, we may conveniently begin with 

 those characters which have been most used in phylogenetic 

 discussions, and proceed to deal with the rest in a definite order. 

 Thus we shall at first confine our attention to a study of the 

 Wings alone, and these will occupy two or more parts of the 

 work. Next to these, we shall take the Mouth-parts. Sub- 

 sequent parts will deal with other imaginal structures; and, 

 lastly, the structure of the larva and pupa will be reviewed. As 

 regards the structure of the egg, and the Embr^^ology, it is to be 

 regretted that so little is known about the latter in the case of 

 the more archaic Orders. As our knowledge stands at present, 

 the evidence available on this point, for the purposes of this 

 paper, is so incomplete, that it can have little bearing upon the 

 main result. 



The investigations into this problem were actually begun 

 about two years ago, and are still going on. I feel that I can 

 safely leave the completion of the more specialiseci parts of the 

 work to a later date; because, if I waited until they were all 

 finished, the main conclusions of this work would not, perhaps, 

 see the light of publicity for some years. The results already 

 attained are, to my mind, of such importance that I have no 

 hesitation in placing them in the hands of the scientific; public, 

 and their value will not be lessened )jy delay in the completion 

 of the whole fabric of my woik. 



BIBLIOGRAPHY. 



1. CoMSTOCK, J. H., 1893. — Evolution and Taxonomy, in "The Wilder 



Quarter Centenaiy Book." Ithaca, N.Y., ISl).'). pp..')?-! 14. iMej-- 

 rick's Law, p. 47). 



2. Handlirsch, a., 1908.— Die Fossilen Insekten. Leipzig, 1908. (Die 



Phylogenie der Pterj'gogenea, viii. Abschnitt, pp. 1228-1318). 



