160 THE COCKROACH : 



has made use of two modes of investigation. The first, or graphic 

 method, in the strict sense of the term, consisted in recording 

 upon a revolving cylinder of smoked paper the respiratory 

 movements, transmitted by means of very light levers of Bristol 

 board, attached to any selected part of the Insect's exoskeleton. 

 Unfortunately, this plan is only applicable to insects of more 

 than average size. A second method, that of projection, con- 

 sisted in introducing the Insect, carried upon a small support, 

 into a large magic lantern fitted with a good petroleum lamp. 

 When the amplification does not exceed 12 diameters, a sharp 

 profile may be obtained, upon which the actual displacements 

 may be measured, true to the fraction of a millimetre. Placing 

 a sheet of white paper upon the lantern screen, the outlines of 

 the profile are carefully traced in pencil so as to give two 

 superposed figures, representing the phases of inspiration and 

 expiration respectively. By altering the position of the Insect, 

 so as to obtain profiles of transverse section, or of the different 

 parts of the body, and, further, by gluing very small paper slips 

 to parts whose movements are hard to observe, the successive 

 positions of the slips being then drawn, complete information 

 is at last obtained of every detail of the respiratory movements : 

 nothing is lost. 



This method, similar to that employed by the English phy- 

 siologist, Hutchinson,* is valuable, because it enables us, with a 

 little practice, to investigate readily the respiratory movements 

 of very small Arthropods, such as Flies or Lady-birds. It has 

 this advantage over all others, that it leaves no room for errors 

 of interpretation. 



Not satisfied with mere observation by such means as these, 

 of the respiratory movements of Insects, the writer has also 

 studied the muscles concerned, and, in common with other 

 physiologists (Faivre, Barlow, Luchsinger, Donhoff, and Langen- 

 dorff), has examined the action of the various nervous centres 

 upon the respiratory organs. The results at which he has 

 arrived may be summarised as follows : 



1. There is no close relation between the character of the 

 respiratory movements of an Insect and its position in the 

 zoological system. Respiratory movements are similar only 



* J. Hutchiuson, Art. Thorax, Todd's Cycl. of Anat. and Phys. 



