148 



HARD WICKE'S SCIENCE-GOSSIP. 



terminate a little above and near to the strongly- 

 marked ends of the pseudo-trachea;. 



These trachea; and the dotted membrane obscure 

 the view of the teeth, and, in many cases, it is only 

 by a particular and careful management of the mirror 

 that it becomes at all possible to discern the thin 

 lines of light or shade that mark the outlines of their 

 bifurcate extremities. 



Further, in mounting the object upon Topping's 

 plan, pressure is used on the head of the fly with the 

 design of throwing the proboscis into position of ex- 

 pansion before being fixed on the slide, and in doing 



As may be seen in the foregoing figure, there are 

 three rows of teeth. These lie one above another, 

 and their free ends crop out between the lines of the 

 pseudo-trachea;. The teeth of the first or upper- 

 most row are simple and strap-shaped chitinous bands, 

 and for a considerable portion of the length of each 

 tooth the band is turned in on each margin, and then 

 for the remainder is flattened out and widened before 

 it is terminated in the thin and knife-edged bifurcate 

 extremity. 



The teeth of the second row differ somewhat in 

 form from those of the first. Each tooth is not a 



Fig. 100. Teeth of the Blow-fly (mag.). 



so a dark reddish fluid generally passes into the 

 proboscis between the membranes and under the 

 teeth, thus giving an additional hinderance to the 

 view required. I had found that prolonged steeping 

 in turpentine will bleach the teeth rather than remove 

 the stain, and only increase the difficulty of examina- 

 tion. Sometimes, however, a case will occur in 

 which this latter difficulty, even without especial 

 caution, will not arise ; then the teeth and pseudo- 

 tracheae will be fairly seen, as in the following figure 

 of a. small portion of one of the lips of the proboscis. 



simple and single strap, but, for about two-thirds 

 of its length, is a divided one, and springs from two 

 different points of attachment, as in the following 

 figure. 



The two bands of chitine join, and are then 

 flattened out and terminated as in the tooth of the 

 first row, but much fainter in colour, and by [no 

 means so easily distinguished and observed. 



The teeth of the third row are similar in structure 

 to those of the second, but only of half their length, 

 and they spring from quite different positions in the 



