THE LIFE CYCLE 



351 



Not all of the body is thus destroyed, however; there are 



preserved little islands o 

 regenerative cells in all the 

 principal parts of the body 

 from which their respective 

 continents will be reformed. 

 In the walls of the stomach, 

 for example, there are grouped 

 rings or masses of little cells, 

 rich in protoplasm, by which 

 the new epithelium of the new 

 stomach will be developed. 

 The undeveloped legs and 

 wings exist in the larva as 

 little buds of active cells, at- 

 tached to the inner face of the 

 body walls. From these legs 

 and wings now grow out, at 

 first beneath the larval skin, to 

 be freed at its last moulting. 

 About the bases .of these 

 organs and from other regen- 

 erative cell masses in the wall 

 itself, the new body wall is 

 developed. Details of these 

 wonderful processes may not 



be studied here, but there are some easily observable phe- 

 nomena, which will help us to understand the main points. 



Study 42. Observations on internal metamorphosis. 



Materials ne^ed: Living larvae and pupae of some 

 dipterous species having red blood* ; preferably of the cone 



*The blood of insects is not red, except in a few forms, such as 

 the so-called "blood worms", that are the larvae of midges (Chir- 

 on omidae), and in some of the larva? of gall midges (Cecido- 

 myidae). 



FIG. 203. Cone galls of 'the willows 

 caused by the gall midge Rhabdophaga 



strobiloides. a, 



produced on 



crook-necked gall produced on Salix 



bebbiana. 



