68 Laboratory Guide in Zoology 



is divided into four parts : the tergite is the dorsal 

 portion, a pleurite is on each side, and the sternite forms 

 the ventral surface. See if you can distinguish these 

 parts. Remember the structure of the segments in the 

 lobster. 



XL — Study the first segment ; that is, the one next to the 

 thorax. Its sternite is not easily seen, but'on each side 

 above you will find a nearly circular cavity covered by 

 a thin membrane. This structure is beheved to serve 

 as an ear. On the side of the abdominal segments 

 find spiracles similar to those on the thorax. Are spir- 

 acles found on all of the segments.' Is there more 

 than one pair on any somite .'' 



XII. — Notice that the somites at the posterior end of the 

 abdomen are greatly modified. In the case of female 

 specimens the abdomen ends in two pairs of pointed 

 processes curving outward. When these are brought 

 together they form a device for burrowing into the 

 ground, and they serve as the ovipositor of the insect. 

 In the male the end of the abdomen is much blunter. 



XIV. — Draw a side view of the grasshopper. 



THE DRAGON-FLY 



Dragon-flies are abundant about ponds in summer. 

 Large specimens serve admirably for showing the general 

 structure of an insect. 

 I. — Find the three great divisions — head, thorax, and 



abdomen — into which the body axis is separated. 



II. — Compare the relative sizes of each of these divisions 

 with the relative sizes of the same parts in the grass- 

 hopper. 



III. — Between which parts does the division line show 

 most plainly } 



