54 Psyche [June 



The need of a satisfactory and uniform nomenclature of these 

 parts is evident. Mr. Nathan Banks, ^ Mr. M. E. MacGregor,^ 

 and Professor W. B. Herms,^ especially, have emphasized the value 

 of these structures with reference to the larvae concerned in myiasis ; 

 the writer^ has for several years been applying this method to the 

 larvae of Syrphidae; and indeed many investigators in recent years, 

 have recognized the necessity of figuring the stigmal plates of the 

 larvae described in a number of Dipterous families. I have no 

 doubt that many of the groups of amphineustic larvae can be spe- 

 cifically diagnosed in the same way. In the various publications 

 touching on this subject a variety of terms have been used. It is 

 with the hope of acquiring uniformity of terminology in the various 

 groups and by subsequent investigators that I have herein compiled 

 and described such of these terms as have come to my attention.^ 



The spiracles, together with the adjacent surface of the segment 

 which bears them are called the stigmal field. The right and left 

 halves of the respiratory organ, which are especially heavily chiti- 

 nized, are each called a stigmal plate. The diagnostic points of 

 chief importance, so far as my observations have gone are as fol- 

 lows : 



(1) Whether the stigmal plates are sessile on the caudal surface 

 of the last segment, or stalked, i. e., elevated at the end of a shorter 

 or longer (sometimes tremendously elongate) tube. 



(2) Whether the two stigmal plates are contiguous or separated. 



(3) // separated, the distajice between the plates: the minimum 

 transverse distance intervening. (MacGregor, Herms.) 



(4) If stalked, or sessile and contiguous, the width of the posterior 

 respiratory organ: the maximum transverse measurement from 

 lateral margin of one stigmal plate to lateral margin of the other. 



(5) // separated, the width of one stigmal plate may be more satis- 



1 Banks, N., The structure of Certain Dipterous Larvae with special reference to those in 

 Human Foods, Bull. U. S. Dept. Agr. Tech. Ser. 22, Jan. 10, 1912. 



s MacGregor, M. E., The Posterior Stigmata of Dipterous Larvse as a Diagnostic Character: 

 with Especial Reference to the Larvse Incriminated in Cases of Myiasis; In Parisitology, Vol. 

 VII, No. 2, June 19, 1914, pp. 176-188, 3 ppl. 



' Herms, W. B., Medical and Veterinary Entomology, The Macmillan Co., 1915, pp. 259, 

 260. 



« Metcalf, C. L., The Syrphid® of Ohio, Ohio Biol. Sur. Vol. I, Bui. 1, June, 1913; Me. Agr. 

 Exper. Sta. Bui. 253, Oct. 1916; and do Bui. 263. Oct. 1917. 



' I am indebted to Professor Charles T. Brues for assistance with the literature on this subject. 



