DISSECTIONS. 173 



has no gizzard. The water-beetle, on the other hand, has 

 a gizzard placed at the end of the oesophagus or gullet, its 

 object being to more completely triturate the food before it 

 passes into the stomach. The gizzard is composed of hard 

 muscular tissue, and nearly always covered internally with 

 hard growths called teeth. 



In Fig. 1 59, A is the oesophagus or gullet, B the gizzard, 

 D the stomach, E the small intestine, while the large oval- 

 shaped sac at the extreme left is the large intestine. 



If the gizzard only is required, the best plan is (after 

 killing) to hold the insect under water, and with the forceps 

 to draw the head from the body. Most of the internal 

 organs will by this means be drawn out, when the gizzard 

 can be detached with the scissors from its place below the 

 gullet, washed, and opened out with knife and needle. 



After having proceeded so far, the student will do well to 

 examine the nervous system, and last of all, when the inside 

 has been cleared out, the segments and spiracles may follow 

 in their turn. 



Insects intended for dissection should never be allowed 

 to become dry, and if they cannot be treated at once they 

 should be preserved in dilute glycerine, dilute acetic acid, 

 or weak spirit, according to what is required of them after- 

 wards. 



The student perhaps may not have patience at first 

 to go through the whole set of dissections from one 

 insect, and, therefore, such objects as the saws of the 

 different saw-flies may be attractive. Several different 

 varieties are shown in Fig. 161. 



The variation in the form of saw from the different 

 species, as illustrated in figure, has been carefully studied 

 and the drawings made by Mr. J. W. Gooch. No. I is the 

 saw of the large green saw-fly ; 2, the black saw-fly ; 3, 

 small black saw-fly ; 4, a brownish saw-fly ; 5, black saw- 



