104 SATURDAY LECTURES. 



wing and join their parent in her war song and house in- 

 vasions, till, after throwing oft" the skin a few times, they 

 have become full-grown, and then with another molt have 

 changed to what are technically known as pupae {g) In 

 this state they are no longer able to do anything but 

 patiently float with their humped backs at the surface of 

 the water, or to swim by jerks of the tail beneath, after the 

 fashion of a shrimp or a lobster. At the end of about three 

 days they stretch out on the surface like a boat, the mosquito 

 bursts the skin and gradually works out of the shell which 

 supports here during the critical operation. She rests with 

 her long legs on the surface for a few moments, till the 

 wings have expanded and become dry, and then flies away 

 to fulfill her mission, a totally different animal to what she 

 was a few hours before, and no more able to live in the 

 water as she did then, than are any of us ! Is it not 

 wonderful that such profound changes should take place in 

 so short a time? Even the bird has to learn to use its 

 wings by practice and slow degrees, but the mosquito uses 

 her newly acquired organs of flight to perfection from the 

 start ! 



In this transformation from an aquatic to an aerial life, 

 the mosquito has first breathed from a long tube near the 

 tail ; next through two tubular horns near the head, and, 

 finally, through a series of spiracles along the wdiole body. 



From a calculation, made by Baron Latour, the mosquito 

 in flight vibrates its wings 3,000 times in a minute — a 

 rapidity of motion hardly conceivable. 



Those who have traveled in summer on the lower ]\Iissis- 

 sippi or in the Northwest have experienced the torment 

 which these frail flies can inflict : at times they drive every- 

 one from the boat, and trains can sometimes only be run 

 with comfort on the Northern Pacific by keeping a smudge 

 in the baggage car and the doors of all the coaches open to 

 the fumes. 



The bravest man on the fleetest horse dares not cross 

 some of the more rank and dank prairies of Northern Min- 

 nesota in June. It is well known that Father De Smit once 



