THK SYRPHIDAE OF OHIO 23 



species is in the character of the posterior stigmata or respiratory organs. 

 These are of a fair size; are alwa3-s exposed in larval as well as pupal 

 stages; present a really surprising variety of characteristics; and, being 

 well chitinized, the characters are tolerably constant within specific 

 limits. In these stigmata one may note the approximate length of the 

 whole projection; its exact width and depth; the extent of elevation of the 

 slit-like spiracles; their exact length and width; their arrangement with 

 respect to each other; the amount of divergence of the two approximate, 

 cylindrical tubes at the extreme tip; the character of spinous and other 

 ornamentation, etc., etc. The nature of the ornamentation between the 

 spiracles varies from .sharp, leaf-like, erect, irregular ridges, to sharp or 

 blunt spines, to hairs or bri.stles, and is of the greatest value. 



It is much to be regretted that in the few cases where immature 

 stages of Syrphidae have been described, these characters have not 

 been noticed or were not considered of sufficient value to be recorded. 

 It is desirable that these few .species be again gone over in this light so 

 that there may be an accurate basis for distinguishing our species. 



The "rat-tailed" larvae doubtless will be found to present sufficient 

 characteristics for specific .separation. Something may be made of the 

 .size, general shape, color and appearance. In this case, anterior spiracles 

 or respiratory cornua are of such a size that careful examination will 

 usually show clearly their microscopic structure, and this may be used. 

 (Figs. 112, ii3of Plate VI, Fig. 132 of Plate VII). The po.sterior respira- 

 tory appendage also will be found to vary in structure and appearance and 

 the pro-legs may vary in number. Another point of which much may be 

 made, I feel sure, is the vestiture of the various parts of the body; the 

 hooks on the pro-legs, tho.se on the .several segments of the "tail" and 

 the character of the ornamentation at the tip of the latter. (Note Figs. 

 ^38, c; 133, 135 of Plate VII) . It is almost certain that the larvae oiMicrodon 

 can be .separated by the characteristics of the reticulate ornamentation of 

 the dorsum, the fringe-like border of the body, the stigmatic pattern on 

 the posterior respirator}' appendage, etc. General size, shape and propor- 

 tions ought to be of considerable use in larvae of this kind where the 

 bod}' is rather rigid and .seemingly must hold to almost a constant position. 



There is such great diversity of structure among the larvae with 

 different habits that until more of them are studied it will be impo-ssible 

 to construct a phylogenetic table. For reasons which are stated in the 

 discussion of larval habits (pp. 38-40), I believe the phytophagous larvae 

 to be most primitive in ha])it and they may be considered the most 

 generalized of the group structurally. It must be remembered of cour.se 



Syrp. 3 



