62 STUDIES OF ANIMAL TYPES 



Directions. A. LIFE HISTORY OF CULEX. The com- 

 mon mosquito lays its eggs in summer, in boat-shaped 

 masses, on the surface of the water in rain tubs, ditches, 

 etc. The egg masses are plainly visible to the unaided 

 eye and appear like small patches of soot floating on the 

 water. Find some, take them into the laboratory, and place 

 them on water in some kind of a jar. Note the shape of the 

 egg mass. Which side of the mass is concave and which 

 side is convex ? Can the individual eggs be seen with the 

 naked eye ? Note that the egg masses appear to be sur- 

 rounded by a glistening film on the under sides. This is 

 due to a layer of air about them. Push the mass 

 beneath the water. Does it sink? Does it get wet? 

 Break up an egg mass and examine the individual eggs 

 under the microscope. What is the shape of an egg? 

 The wiggler emerges from the larger end of the egg. 

 On which end do the eggs stand when floating in the 

 mass? Why? 



Make a drawing of the egg mass and of a single egg. 



In a day or two, if the room is warm, the eggs in the jar 

 will have hatched. Note the length of time it took them 

 to hatch after being brought into the house. Take out some 

 of the young larva? and examine them beneath the micro- 

 scope. It will be well to put some cotton fibers under the 

 cover glass to entangle the wigglers, in order to keep 

 them in the field of vision. Note the transparent body 

 divided into head, thorax, and abdomen. Note the two 

 dark spots, eyes, on the head. Note the two antennae with 

 bristles on the ends. Note the bunches of dark hairs on 

 the head near the mouth. Is the thorax any larger than 

 the abdomen? Count the segments in the abdomen. 

 On the caudal end of the abdomen note the long tube. 



