THE ORGANS OF CIRCULATION AND RESPIRATION. 159 



where the spiral thread ceases, and where the exchange of 

 gases through the wall of the tubule becomes comparatively 

 unobstructed. Such a tubule is about '0001 in. diameter. If 

 we may extend to such tubules the laws which hold good for 

 the flow of gases in capillary tubes of much greater diameter, 

 the quantity of air which might be transmitted in a given time 

 by muscular pressure of known amount can be determined. 

 Suppose the difference of pressure at the two ends of the tubule 

 to be one-hundredth of an atmosphere, and further, that the 

 tubule is a quarter of an inch long and "0001 in. diameter. 

 The tubule would then be cleared out every four seconds. Such 

 a flow of air alon^ innumerable tubules might well suffice for 



o <-> 



the respiratory needs of the Cockroach. Without laying too 

 much stress upon this calculation, for which exact data are 

 wanting, we may be satisfied that an appreciable quantity of 

 air may be made by muscular pressure to flow along even the 

 finer air passages of an Insect.* 



Respiratory Movements of Insects. 



BY FELIX PLATEAU, PROFESSOR IN THE UNIVERSITY OF GHENT. 



The respiratory movements of large Insects are in general 

 very apparent, and many observers have said something about 

 what they have seen in various species. It is only since the 

 publication of Rathke's memoir, however, that precise views 

 have been gained as to the mechanism of these movements. 

 This remarkable work, treating of the respiratory movements 

 in Insects, the movable skeletal plates, and the respiratory 

 muscles characteristic of all the principal groups, filled an 

 important blank in our knowledge. But, notwithstanding the 

 skill displayed in this research, many questions still remained 

 unanswered, which required more exact methods than mere 

 observation with the naked eye or the simple lens. 



The writer, who was followed a year later by Langendorff, 

 conceived the idea of studying, by such graphic methods as are 

 now familiar, the respiratory movements of perfect Insects. He 



* For an explanation of the physical principles involved in this discussion, and 

 for the calculation (based upon our own assumptions), we are indebted to Mr. A. "W. 

 Ptiicker, F.R.S 



