- 41 



At the side one of these folds encloses the basal chitinous support of the maxillae 

 as can be seen in pi. 2, fig. 1, * and A', where the basal supports of the maxillae 

 are lettered #, and the folds of the labium /' and I". In CWe.r the same relative 

 position and connection of parts are found, as can be seen in pi. 1, figs. 9 or 15, 

 where the pharynx and its muscles are surrounded above by the clypeus (c), 

 extending, at the sides, into the bases of the maxillae (mx) and of the maxillary 

 palpi (mp), and continuing beneath into the walls of the basal portion of the labium. 

 In EristaMs and Musca, when the basal half of the proboscis is retracted, the 

 conditions are relatively the same as in Bombylius. (Compare pi. 3, fig. 2, and 

 pi. 4, fig. 3, with pi. 2, fig. 3.) The clypeus (c on each pi.) extends downward, 

 from the frontal angle (rf) of the head, to the middle joint of the proboscis; at 

 the sides, as can be seen in figures of numerous sections, the bases (.<) of the 

 maxillae, where maxillae exist, are in the base of the labrum (7) or in its fold (/'). 

 The question, whether, or not, the portion represented in section in pi. 4, fig. 1, 

 /?', x, is the hornolog of a basal portion of a maxilla is left for further con- 

 sideration. 



Having discussed the surroundings and functions of the fulcrum in Culex, 

 Bombylius, Eristalis and Musca, the question remains, what is the fulcrum itself, 

 homologically considered? Repeating, in some cases, what I have already said, 

 in earlier parts of this paper, I will briefly state the opinions of several authors 

 on this question. Gerstfeldt 3 figured the fulcrum of Musca, without assigning it 

 a special name, and apparently without discovering that it was, strictly speaking, 

 an internal organ. He considered the fulcrum to be made up of the maxillae, 

 for the most part, united with the mandibles above and with the subnientum of 

 the under lip beneath. The incorrectness of Gerstfeldt's views of the construction 

 of the fulcrum are evident when one sees, as already explained, that it is only 

 the outer sheath around the fulcrum that is continuous with the under lip, and 

 that the bases of the maxillae lay entirely independent and outside the walls ol 

 the fulcrum. The use of the name fulcrum, probably originated from the following 

 remark of Lowne 23 (p. 42): "Although I believe this organ is homologous to the 

 fulcrum in bees, I prefer the term pharynx, from its double connection with the 

 mouth and oesophagus, as well as its peculiar function." Macloskie 24 says (p. 154) : 

 "One of Lowne's terms for it (pharynx) is incorrect; it is rather a case 

 surrounding the pharynx. I shall refer to it by the name fulcrum." Macloskie 

 later (p. 159-160) expresses the view that the "mid-segment" of the so-called 

 proboscis, " is the true base of the fly's proboscis ", and homologizes the fulcrum 

 with the endocranium of the cockroach (Blattd) he also says of the fulcrum 

 "It seems to be general indiptera; even the mosquito possesses it," but he does 



