37 



The structure and functions of the fulcrum, and the minute structure and 

 mode of use of the pseudotracheae are left for further discussion later. 



Leaving the part of this paper which is more exclusively devoted to the 

 descriptions of the structure and arrangement of the mouth-parts and suctorial 

 apparatus of the four diptera Culeu, Bombylius, Eristalis and Musca, which I have 

 studied, I turn to the portion of my paper devoted to the 



COMPARISON OF THE MOUTH-PARTS AND SUCTORIAL APPARATUS 

 IN DIFFERENT FAMILIES OF DIPTERA. 



In this division of my paper, while I shall, for the most part, make use of 

 results derived from my own examination of Culex, Bombylius, Eristalis and 

 Miisca, for these four genera make a fine series for most purposes of comparison, 

 I shall not hesitate to take advantage of the results of the researches of others, 

 so far as I think them trustworthy and suited to my purpose, but, in all cases, 

 giving credit, as far as possible, to those from whom I obtain anatomical facts. 

 I shall try, in this portion of the treatment of my subject, to present briefly, 

 together with my own ideas, the views, theories, homologies and nomenclature, 

 which have been adopted by various authors for the mouth-parts of diptera, so 

 far as their views pertain to parts under my consideration. 



The first organ which I shall examine comparatively in this paper is the 

 fulcrum. In Eristalis, the fulcrum (side view, pi. 3, fig. 7; cross-section, fig. 1, 

 ', d'fpf) consists of a hollow frame of chitin, comparable to a somewhat 

 irregular, much compressed, truncated cone, with a deep sinus in each of the 

 flattened sides of its larger, or basal, end. This fulcrum is suspended, by the 

 longer of the two processes (fig. 7, d') of its basal end, in the anterior angle 

 (fig. 1, d~) of the front of the head, - with its apex reaching nearly to the 

 middle joint of the proboscis, - in such a way as to swing on the point d as 

 an axis. In figs. 2 and 3 (of pi. 3) it would occupy the space filled by the 

 pharynx (p) and the pharyngeal muscles (pw); pendulous around the point d, 

 in the extension and retraction of the proboscis. The under, or ventral, portion 

 of the inside of the fulcrum is occupied by the pharynx (fig. 1, e', p); its upper, 

 or dorsal, portion by the pharyngeal muscles (pm). In Musca vomitoria the 

 fulcrum (in cross-section, pi. 4, fig. 4) is of similar general outline as in 

 Eristalis, as can be seen in pi. 4, figs. 2 and 3, where it would occupy the 

 space filled by the pharynx (p) and the pharyngeal muscles (/>w); its posterior 



