78 LABORATORY WORK. 



a long femur, next an almost equally long tibia, and lastly 

 a several-jointed foot or tarsus. Notice how freely the 

 head moves upon the prothorax by means of a flexible 

 'neck.' Separate the prothorax from the head and from 

 the mesothorax and draw it from the side. 



Study meso- and metathorax together. Notice that on 

 the back the line between these somites is very distinct; 

 trace this line upon the side, and thence to the ventral 

 surface. Do you notice any other lines which seem to 

 divide meso- and metathorax? Can you trace them on all 

 surfaces? Do you find any spiracles in this region? How 

 are the legs related to the somites? Can you recognize in 

 each the same parts found in the pro thoracic legs? Where 

 are the wings? Are they alike? What is the prevailing 

 direction of the ribs or 'veins' in them? Can either pair 

 be folded like a fan? Is there anything to protect the 

 hinder pair when at rest? 



Draw a side view of meso- and metathorax, inserting ex- 

 panded wings, legs, etc., and noting especially the spiracles 

 and the lines separating the somites. 



Considering the thorax and tip of the abdomen of the 

 grasshopper, do you find anywhere a segment bearing 

 more than a pair of jointed appendages? * So far as your 

 present knowledge goes, would you be justified in saying 

 that a pair of jointed appendages indicates a somite of 

 the body? (Savigny's law.) 



Notice that the head is made up of a large solid piece 

 (epicranium) , to which are attached various movable por- 

 tions. On either side of the head is a large compound eye, 

 With a sharp knife slice off one of these eyes and examine 

 it under a low power of the microscope. Why is it called 



* For reasons which cannot be discussed here, the wings of grass- 

 hoppers, etc., are not considered as jointed appendages. 



