188 Mr. E. E. Austen on the 



(such as Sargus, Chloromyia, and Actina), as well as the 

 agreement in the mode of pupation, has indeed attracted the 

 attention of most authors who have studied the life-history of 

 the various species. Thus, in 1828, von Roser (loc. cit. 

 p. 188) declared the larva of Xylophagus varius {Xylomyia 

 varia), Mg., to be very similar to that of Stratiomys chamce- 

 leon, excluding the tubular tail ; Westwood writes (' Intro- 

 duction ' &c. ii. (1840) p. 535) :— " The genus Subula, as 

 discovered by M. van Roser and the Rev. F. W. Hope, has a 

 metamorphosis exactly like Sargus, the pupa being enclosed 

 within the unaltered larval skin, but the transformations of 

 the typical Xylophagi are quite different" ; Dufour (loc. cit. 

 p. 7 (1847)) states that the larva of Sargus Reaumurii, F. 

 (= Chrysonotus bipunctatus, Scop.), appears to belong to the 

 same class as that of Subula citripes, Duf. ; and Perris (Ann. 

 Soc. Ent. Fr. sex. 4, t. x. (1870) p. 206) alludes to the close 

 resemblance in outward appearance between the larvae of 

 Subula and those of Pachygaster and Sargus. The agree- 

 ment in general appearance and character of the integument 

 between larvae of Xylomyia and those of Chloromyia or Actina 

 must in fact strike anyone, and to attempt to argue that such 

 a remarkable external resemblance is due to mere conver- 

 gence, brought about by adaptation to a similar mode of life, 

 is manifestly out of the question. To refute such a sugges- 

 tion it is only necessary to compare a larva of Xylomyia with 

 that of Xylophagus or with any of the other dipterous larvae 

 to be found in the mouldering stumps of dead trees. It is 

 true that the larvae of Xylomyia appear to be amphipneustic, 

 while those of Stratiomyidae in general are peripneustic; but, 

 according to Brauer, the number and position of the stigmata 

 is a very variable character, which has arisen by adaptation 

 in so far as these apertures are peripheral or merely polar. 

 Moreover, as I have shown above, the larva of Xylomyia 

 appears to exhibit distinct vestiges of peripheral stigmata. 



With reference to the importance of insect larvae as indi- 

 cating affinities, Brauer writes * : — " To contemplate earlier 

 developmental stages of animals is, however, to cast a glance 

 at their pedigree, which is otherwise beyond our reach, and I 

 have already shown in another place (" Betrachtungen iiber 

 die Verwandlung der Insekten im Sinne der Descendenz- 

 theorie.— II.," Verb. z.-b. Ges. Wien, 1878, p. 151 etsea.) 

 that even such acquired larval forms as those of the insects 

 are adapted for this purpose because they have become heredi- 

 tary." 



There is no necessity to repeat the arguments (drawn from 

 * Denkscbr. k. Akad. Wiss. Wien, Rd. xlvii. (1883) p. 3. 



