BROOK LIFE. 



155 



inch in diameter. A single mass contains from two 

 thousand to three thousand eggs. When the larvae 

 hatch they at once find their way into the water, 

 where they remain until full grown. 



The best time to study this insect is late in the 

 spring and early in the summer, for at this season all 

 stages of it can be found. Try to get larvae, pupas, 

 adults, and eggs, and preserve them in your collec- 

 tion under a copy of the following label :- 



Order NEUROPTERA (Neu-rop'te-ra). 

 Family SIALID/E (Si-al'i-dae). 



The adult dobson is known as the horned Cory- 

 dalis, its scientific name being Corydalis cornnta. 



THE STRUCTURE OF THE DOBSON (School \Vork\- 

 Put a larva in a cyanide bottle one or two hours be- 

 fore it is needed for study, as it requires considerable 

 time to kill these insects. 



1. Lay the specimen on its back and make a draw- 

 ing of the ventral surface. 



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2. Name the parts and appendages of the body 

 shown in this view. The long, tapering appendages 

 on the sides of the abdomen may be termed the 

 lateral filaments ; the tufts of hairlike appendages 

 near the bases of the lateral filaments are tracJieal 

 gills, and at the hind end of the body there is a pair 

 of prolegs. Each proleg is furnished with a pair of 

 claws. 



Note that in addition to the tracheal gills this 

 larva has well-developed spiracles. Make a drawing 

 of a spiracle as seen through a lens. Note especially 

 the lid by which the opening of the spiracle is closed. 

 State the number of spiracles and the position of 



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