104 



HARDWICKE'S SCIENCE-GOSSIP. 



recognized at a glance. As flies of the genus 

 Tetanocera have mouths of the normal shape, 

 we have selected them for illustration and de- 

 scription. 



Eig. 53 'is a drawing of the mouth of Tetanocera 

 Hieracii magnified 45 diameters, and viewed as a 

 transparent object to show its muscular action, 

 which, as it is difficult to understand, we describe 

 somewhat at length. Since everybody is not versed 

 in anatomical terms, we would premise that a 

 muscle is fixed to the skeleton (or to those portions 

 of the animal which serve as the skeleton) by two 



spectively the exsertor and retractor muscles of the 

 mouth. The figure shows the pair b contracted; 

 consequently the mouth is pushed out from the 

 head. If the muscle c were similarly contracted, 

 the pair b would relax, and the mouth be with- 

 drawn. At a are the pharyngeal muscles. They 

 arise from the top of the pharynx, and are inserted 

 into the plate r, fig. 54. (Shown in fig. 53, but not 

 lettered.) It forms the roof of the mouth, and it is 

 joined to the sides of the pharynx. It has a certain 

 limited up-and-down motion, and it is shown nearly 

 shut in fig. 53, and wide open in fig. 54, as if for the 



Fig. 53. Mouth of Tetanocera, x 45 diams., as a transparent object : ph,ph, Pharynx; Ibr, Labrum or upper lip;/, 

 one of a pair of fulcra which move it; I, Lingua or tongue; la, Labium or lower lip ; mt, Mentum;/", Processes 

 which terminate it ; d, d", edge or rim of the oral cleft ; ce, (Esophagus ; sd, Salivary duct ; v, Valve in the same. 

 Names of the muscles, and their points of origin and insertion : — b, Exsertors of the mouth, arising from the rim 

 of the oral cleft at d, and attached to the processes of the pharynx ; e, Retractor of the mouth, from d" to mt ; a, 

 Pharyngeal muscles, from top of pharynx to the roof of the mouth ; e, Depressor of the labium, from tip of pharynx 

 to e ; g, Elevator of the labrum, from apex of the pharynx to end of the fulcrum f ; mt. Muscle of the mentum, 

 from its base to its tip/" ; k, Transverse muscle of the mentum, from e to k. 



points only, at one of which it is said to " arise," 

 while at the other it is "inserted"; and further, 

 a muscle pulls its point of " insertion " or " attach- 

 ment " towards the point where it has its origin, 

 is. " arises." The mouth of a fly has three joints, 

 and the part which first attracts our attention 

 is the pharynx, which forms the basal joint 

 {ph, fig. 53, and shown in section at fig. 54). A 

 good idea of its shape may be obtained by cutting 

 an isosceles triangle out of a piece of paper, 

 folding it down the middle, and fastening toge- 

 ther the two corners which possess the equal 

 angles. Our model pharynx, however, will not 

 possess the two posterior " processes," nor the 

 long and narrow chitonous plate which moves up and 

 down between its sides. To the processes are 

 attached a pair of muscles, I, which arise from the 

 rim of the oral cleft at the point d ; at d", on the 

 opposite side of the rim, arises a muscle c, which is 

 inserted at the base of the mentum. These are re- 



passage of food. The raising and lowering of this 

 plate r produces suction, and it is moved, of 

 course, by the muscles marked a in both figures. 



At Ibr is the upper lip or labrum, which when at 

 rest fits tight over the labium. It consists of an 

 inner and an outer plate connected by transverse 

 muscles (see figure). The inner plate is continuous 

 with the plate r, as the roof of the mouth. At / 

 is shown one of the fulcra which move the labrum. 

 There are a pair of them, one on each side, and 

 they are articulated to the base of the outer plate. 

 They are the homologues of the maxillae in Syr- 

 phidse and other flies. At the top of the pharynx 

 arises a pair of long muscles, g, inserted where the 

 fulcra join the labrum. These muscles elevate that 

 organ, as shown in the drawing : attached to the 

 other end of the fulcra are the muscles h, which 

 depress it ; while another muscle (only faintly 

 drawn), which has its origin at the tip of the 

 pharynx, aids g in raising it. These three pairs of 



