77//' )F TN8Ed 81 



il<i flu- tympanum and 1 1 1 • - membranou the 



base <»r the hind legs. When the tergum or dorsal pot 

 of the abdomen falls ami the pleurum contracts, t 

 acles open; their opening is nearly bul nol alv ictly 



co-ordinated with the contract ■( the pleurum, but 



: rule it is. There were sixty-five contractions in a 

 minute in a locusl which had been held between the lit . 

 about ten minutes. It was noticed that when theabdomen 

 expanded, the air-sacs in the first abdominal ring contracted. 

 The air passes into the spiracles during the expansion of the 

 abdomen. In most insects, says Plateau, only the expira- 

 torymovement is active; inspiration is passive, and effected 

 by the elasticity of the body-walls.* 



It is evident that the enormous powers of flight possessed 

 by the locust, especially its faculty of sailing for many hours 

 in the air, are due to the pi of these air-sacs, which 



float it Hi' in the atmospheric sea, increasing the hulk of 

 the body, without rendering it heavier. Other it tvith 



a powerful flight, as the bees and flies, have we] >ped 



air-sacs, but tiny are less numerous. It will be seen that, 

 mice having taken flight, the locust can In; f up in 



the air, constantly filling and refilling its internal buoj 

 balloons with little muscular exertion, and thus be borne 

 along by favorable winds to its destination. It is evident 

 that the piece-- of respiration can lie best carried oil in 

 clear, sunny weather, and that when the sun sets, or the 

 weather is cloudy and damp. it< powers of flight are less- 

 ened, owing to the diminished power of respiration. 



The Senses of Insects. I: difficult to explain man] 

 tiie actions of insects, from the fact that it is hard for i 

 appreciate their instincts and general intel! That 



they have sufficient intellectual powers to enable them to 

 maintain their existence maybe regarded mi. Hut 



insects differ much in intelligence, and 

 perfection of the organs of sense. The i 1 1 1 > : in- 



* See Miall and Dennj > " The Cockroach," p. 



