CHAPTER IV 



* 



THE DEVELOPMENT OF INSECTS 



23. Metamorphosis. The changes which an insect 

 undergoes during its progress from the newly hatched 

 form to the adult vary in degrees of complexity and are 

 commonly grouped into two types. The more simple type 

 is spoken of as incomplete metamorphosis or direct develop- 

 ment. The word metamorphosis signifies change in form. 

 Therefore, the correct inference is that the change in form 

 in this type of development is not complete. 



The second and more complex type of development is 

 that known as complete metamorphosis or indirect develop- 

 ment. In this case there is a complete change in form and 

 appearance between the earlier stages and the adult. 



24. Direct Development. A description of the devel- 

 opment of the grasshopper is commonly given to illustrate 

 the direct type. Here, as in practically all insects, the 

 first stage is the egg. From the egg hatches a form which 

 may easily be recognized as a young grasshopper, even 

 though the proportions are distorted and there are no 

 wings. The form just hatched is known in this case as a 

 nymph, and the same term is applied to all the succeeding 

 stages of the insect before it reaches the final or adult 

 stage and becomes what is called an imago. 



Each succeeding nymphal stage resembles the adult 

 form more than did the one preceding it. In one of 

 the earlier stages the wings make their appearance in 

 the form of small pads on the thorax. These become 



28 



