39 



more definitely the pumping organ in the basal half of the proboscis, " which" 

 he writes (p. 20), " may be indeed the real pump of the whole machine." * 

 Lowne 2:? (p. 41-42) gives an excellent description of how the parts of the fulcrum, 

 which he calls the pharynx, act in pumping. A second function of the fulcrum 

 in Musca and Eristalis, and one which will be seen later to be less constant 

 throughout the diptera than the first function, is to support and control the 

 motions of the basal half of the proboscis, of course controlling through its basal 

 half many of the motions of the whole proboscis. On the posterior ventral pro- 

 cesses of the fulcrum (pi. 4, fig. 2 and 3, ~) are inserted muscles, which have 

 their origins in the anterior, lateral part of the head; these muscles, by their 

 contraction, project the base of the proboscis, by revolving the fulcrum about the 

 point d, where it is attached. 



The next question which naturally arises is, whether the fulcrum, more or 

 less completely developed, is found, or not, in Cule.r. and Bombylius. A hasty 

 examination of the median longitudinal section through the head of Bombylius 

 (pi. 2, fig. 3) shows that the portion comprised, in section, by the pharynx (/>) 

 and the pharyngeal muscles (pm) is an exact morphological counterpart of the 

 section of the fulcrum in Eristalis and Musca. (Correspondingly lettered in pi. 3 

 and 4, figs. 2 and 3.) A cross-section of the fulcrum of Bombylius, near its 

 distal end (pi. 2, fig. 1, I', //) shows that it consists, like the corresponding 

 section in Musca, of the upper and under walls of the pharynx, extending upward 

 and divergent, from each side of the pharynx, and having between its diverging 

 walls the pharyngeal muscles (pm). The differences in structure between this 

 fulcrum of Bombylius and that of Musca and Eristalis are such as are due to 

 the fact that the proboscis of Bombylius is not extensible, and, consequently, 

 that its fulcrum need not be movable about an axis at d (pi. 2, fig. 3). This 

 absence of motion of the fulcrum around an axis allows the fulcrum to be less 

 independently suspended in the head than it otherwise would be; its upper side 

 consequently fails, its lateral chitinous walls are attached to the anterior wall 

 of the head, and the pharyngeal muscles have their origin on the wall 

 of the head. The distal extremity of the fulcrum of Bombylius serves, as it 

 does in Musca, for attachment for the bases of the labrum-ephipharynx and 

 hypopharynx. Here, then, in Bombylius, the fulcrum retains its essential 

 anatomical characters, and its function as a suctorial organ; but is less 

 independently movable than in Musca and in Eristalis, and its position is inside 

 the head. 



* "... Welches wol die eigentliche Pumpe der ganzen Machine seyn mag." 



