MICROSCOPE IN-DOORS. 69 



structed. This insect has a gizzard, and at the 

 upper part it is beset with six conical teeth (Fig. 

 210, a, PL 8), which, working together, reduce its 

 food to a pultaceous mass previous to digestion. 

 When cut open, the position and relations of these 

 teeth (6) can be easily seen. The gizzard of the 

 cricket is also supplied with teeth (Fig. 211, a, 

 PL 8): it has three longitudinal series of teeth, and 

 each row in each series contains seven teeth (5). 

 The family of insects to which the cricket belongs 

 (Orthoptera\ afford several other instances of the 

 same kind of structure in the gizzard. It will be 

 interesting to compare these teeth of the insects 

 with those of the inollusca and the wheel ani- 

 malcules. 



We must satisfy ourselves with having shown 

 the student the way to cultivate a large field of 

 interesting and instructive phenomena in the insect 

 world, without going farther into detail. 



The tissues or textures of which animals are built 

 up or made of, may be easily procured in-doors. 

 We have spoken of the hard parts which form the 

 outer skeleton of the lower animals, as the mol- 

 luscs, crabs, and fishes ; the internal skeleton of 

 the higher animals affords a not less interesting 

 field of research. If we take a piece of bone, and 

 having ground it so fine that we may examine 

 it with transmitted light under the Microscope 

 (Fig. 222, PL 8), we shall find it composed of a 

 number of minute insect-shaped cells, surrounding 

 an open canal. These cells, which are called 

 lacunce, and their little branches canaliculi, are 

 modifications of the cells found in fishes' scales 

 (Fig. 171, PI. 6). 



These curiously shaped cells differ in size and form 

 in the various classes of animals belonging to the 

 sub-kingdom Vertebrata } and thus a small portion 



