8 



ZOOLOGY 



certain useless or waste by-products, and these have to be 

 carried away. So in the living bodj-, which is a sort of chemical 

 la})oratory, there are many waste products, and these have to 

 be taken from the tissues where they first appear and conveyed 

 to the outside of the body. In insects these waste products are 

 picked up from the bodj'-fluids by means 

 of tubes that empty into the intestine. 

 From tlie intestine they pass with the un- 

 digestible food matter to the outer world. 

 Reproduction in the Cricket. — A 

 varietjr of accidents — starvation, floods, 

 severe cold, attack by other organisms 

 — kill vast numbers of crickets each year. 

 The normal number is maintained only 

 by reproduction, or the production of new 

 ones. While in some animals reproduc- 

 tion takes place by a division of the 

 parental l)ody into two nearly ecjual in- 

 dividuals, in the higher animals usually 

 only a piece of the parent — called a germ- 

 cell — is set free, and the offspring has to 

 Fig. 7. — View of ar- develop from this Small bit. Also in most 



rangenient of tracheal • i i j i m , 



or breathing tubes in anunals, t)ut by no means all, two germ- 

 tho cockroach. After cells (usuallv, but not alwavs, from differ- 



Miall and Denny. .... 



ent mdividuals) must meet and unite 

 before development begins. To provide food for the de- 

 veloping young, one of the two germ-cells is of large size 

 and full of foodstuffs. It is called the egg, and the 

 individual producing it is called a female. The other germ- 

 cell is not stuffed ^Wth food, but is active and goes into 

 the egg and through to its centre; it is called the sperm- 



