76 ANIMAL ACTIVITIES. 
The ovipositor differs from that organ as we have 
seen it in the cricket and grasshopper in having, in 
addition to the grooved sheath through which the eggs 
pass, a pair of lances which pierce the insect it wishes 
to paralyze or kill. The paralysis is probably caused 
by a bit of formic acid which is secreted by a small 
gland in the wasp’s abdomen and injected into the 
body of her victim. 
The sting, then, in this case as in the bee and other 
hymenoptera, is a modified ovipositor. 
The care with which the wasp cleans its body and 
performs its toilet is worth noting. In fact, many 
things may be learned by watching one of these intelli- 
gent little workers. 
The Dragon-fly. To study insects which spend a 
part of their life in the water an aquarium is helpful and 
pays well for the trouble it costs. 
To study the young dragon-fly one should visit a 
pond or pool of fresh water, provided with a small] net 
and a supply of fruit-jars. The young dragon-flies 
may be recognized by their flat square heads, their 
rudimentary wings, and their six strong legs. They 
frequent the bottom of the pool in which they live and 
their color protects them from observation, but careful 
watching will soon reveal their presence. One sweep 
of the net will sometimes bring several nymphs to the 
collector’s jar. One must at the same time collect 
some aquatic plants to keep in his aquarium, and also 
a supply of small insects for dragon-fly food. A little 
mud from the pool with some submerged sticks and 
leaves will furnish insect-food for several days, after 
which a fresh supply should be provided. With a little 
sand in the bottom of a jar, a few growing water-plants, 
and a supply of dragon-fly nymphs of varying sizes, we 
are ready to learn something of the life-history of the 
mosquito-hawks, as dragon-flies are sometimes called. 
While collecting the young, one is likely to see the 
adult females dipping the tip of the abdomen beneath 
