APR. 19, 1923 PROCEEDINGS: ENTOMOLOGICAL SOCIETY 161 
insects and their ability for considerable contraction of the body, and first 
thought that Dr. Bovine was right in supposing that the expiration of the 
air from the tracheae was brought about by a complete compression of this 
entire system, following a simultaneous contraction of all the body muscles, 
and that the inhalation followed when the elastic tracheal walls again ex- 
panded as a result of relaxation of the muscles. Later he reconsidered 
this idea and could hardly believe that the pressure of the muscles was strong 
enough to affect the total compression of the whole system with all its fine 
tracheal branches. Therefore he began to consider another way in which 
the respiration could be performed. The only other possible alternative 
would be respiration by a diffusion of the air through the fine branches of the 
tracheal tubes. Before he started the research work he thought out as a 
working base the following formula for respiration through diffusion: Res- 
piration is equal to a constant representing the amount of oxygen which in 
a chosen unit of time, for instance one second, multiplied by a fraction, the 
numerator of which is the difference in pressure of the oxygen in the atmos- 
phere and at the bottom of the air tubes multiplied by the total transverse 
area of the tracheal tubes, the denominator of which is expressed by the length 
of the air tubes of the whole tracheal system. In insect larvae, for instance 
in a Cossus larva, the amount of oxygen absorbed in a certain unit of time 
can be measured by respiration experiments, and to determine the average 
lengths and the total of width of the tracheal system the author had filled 
the tracheal system of a Cossus larva with a solution of stained fat and then 
separated the complete tracheal system by dissolving all the tissues with 
Pepsin-muriatic acid. The result of this preparation of the tracheal system 
was shown on the screen. By measuring length and total width of the tra- 
cheal system of different larvae and knowing the amount of oxygen diffused, 
he found that a difference of about 2 per cent in the oxygen outside and inside 
was all that was necessary for the sufficient supply of oxygen through a proc- 
ess of diffusion. This result was substantiated by direct measurements of 
the diffusion of the air in the tracheae of Cossus. By experiments he could 
also prove that special respiration movements were not ‘present and also 
that even a forceful contraction of the entire musculature of the body wall 
would only result in a slight and unimportant expiration of air. The results 
acquired were generalized to apply to most larvae and probably all pupae, 
to almost all very small insects, and to all Arachnids and Myriopods. 
The most difficult problem is to supply air in the long slender organs, like 
the legs of many Arachnids. It has been shown by Dr. H. F. HANssEn, in 
Copenhagen, that there are extra spiracles on the tibiae of long legged 
Opiliones. In the larger adult insects the length of the tracheal tubes is 
often considerable, and respiration through diffusion alone would not suffice. 
In these forms an additional mechanical ventilation takes the place of the 
larger main tracheal tubes and the air sacks. 
The ventilation-tubes differ from the diffusion tubes in being easily com- 
pressed; often their cross section is narrowly elliptical. Similar ventilation- 
tracheae and a mechanical respiration are present in the water beetle larvae 
with the single pair of spiracles at the end of the abdomen. In connection 
with investigations of the large Dytiscus larvae, Dr. Krogu had measured 
the normal amount of exhaled air, the maximal amount of exhaled air by 
voluntary respiration, the greatest possible amount of exhaled air, or the vital 
capacity, and the total area of the tracheal system at the time when the larva 
was in its normal inhalation or resting position., In a larva weighing 1.7 
grams he found that the total area of the system amounted to 107 mm.°* 
