ELEMENTS OF ZOOLOGY 



CHAPTER I 



THE CRICKET: A STUDY OF THE ANATOMY AND 

 PHYSIOLOGY OF INSECTS 



The cricket is a thing that can move of itself, can feed and 

 grow and produce young hke itself ; consequently it is 

 hving. It has numerous external parts and 

 complex internal organs ; hence it is an or- 

 ganism. It moves freely from place to 

 place, and devours and digests sohd food ; 

 and so it is an animal (Fig. 1). 



An animal is a complex machine built up 

 of a remarkable substance called protoplasm 

 and of materials that it produces. Proto- 

 plasm looks like a jelly, but it is really itself 

 highly organized, so that the animal ma- 

 chine differs from man-made machines in 

 having a mechanism inside the very substance of which its 

 parts are made. Some idea of protoplasm may be got from 

 Figure 2, which shows a bit of it existing as a free Uving 

 animal with no other organs than those essential to all proto- 

 plasm. But in higher animals the body gains a great size ; 

 contains huge spaces that are filled with water or air; and is 

 built up of membranes that cover the surface of the body (the 

 skin) or hne the food-canal and body-cavities, of masses 

 that support the other parts (the skeleton) or are used for 



Fig. 1. — Cricket, 

 immature. Nat. 

 size. Photo, by 

 W. H. C. P. 



