Plate XIV 



Fie. I. 



Fig. 





Fig. 3. Fig. 4. 



I is a photograph ( x 66) of the oral surface of the erected suctorial disc of a blow-fly. 

 The pseudo-trachere and anterior and posterior common collecting channels are well seen. 



. 2 is a photograph of proboscis marks produced by a fly feeding on a thin layer of Indian 

 ink spread on glass. The position ot the anterior cleft is indicated in every proboscis 

 mark. The marks show that in each case the proboscis has been firmly and evenly applied. 



, 3 is a photograph ( x 77) of a portion of a proboscis mark left by a fly attempting to suck 

 up a layer of partially dried Indian ink deposited on glass. The outline of the suctorial 

 disc is clearly shown. The marks indicating the position of the longitudinal sulcus are 

 very narrow, showing that the prestomal cavity was almost completely closed. The lines 

 of the pseudo-trachete are marked by double rows of regularly placed clear oval areas, 

 separated by thin black lines. Each of these areas, from which the pigment has been 

 removed by suction, represents the space covered by an interbifid groove. 



, 4 is a photograph of part of a proboscis mark similar to that shown in Fig. 3, more 

 highly magnified ( x 770). The longitudinal axis of each pseudo-trachea is marked by a 

 zigzag black line, showing that the longitudinal fissure was closed. On each side of the 

 zigzag black line are clear areas produced by the removal of the pigment through the 

 interbifid grooves. Their shapes are very clearly defined. The way in which this 

 pattern is produced can be readily comprehended by reference to PI. XIII, Fig. i 

 (left-hand side). The broad black lines, separating the clear areas, represent the inter- 

 pseudo-tracheal plane areas of the disc. 



(From Graham-Smith, Journal of Hygiene, 1 9 1 1 . ) 



