[154] 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. Rücker, F.R.S. _Respiratory Movements of Insects._ By FÉLIX 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 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, consisted 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 physiologist, Hutchinson,[155] 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. [155] J. Hutchinson, Art. Thorax, Todd’s Cycl. of Anat. and Phys.