1921] Muttkowski: Respiration of Insects 153 
In the third phases of that study, the distribution of copper in insects, 
the following list of animals were incinerated. (Numbers refer to num- 
ber of separate incinerations, not to number of specimens): 
Coleoptera: Dytiscus, 19; Gyrinus, 1; Harpalus, 1; Leptinotarsa, 1. 
Hymenoptera: Apis, 2; Bombus, 1; Polistes, 2; Formica, 1. 
Lepidoptera: Pieris, 4; Noctuide, 2. 
Diptera: Musca, 4; Stomoxys, 2; Tachinid, 1; Stratiomyia, 1. 
Hemiptera: Belostoma, 17; Ranatra, 1; Notonecta, 3; Gerris, 1; Corixa, 2; Aphis, 
1, Leptocoris, 2. 
Odonata: Anax and Aeshna, 4; Anax, 2; Aeshna, 15; Sympetrum, 4; Libellula, 4; 
Enallagma, 6. 
Ephemeride: Several spp., 1. 
Trichoptera: Several spp., 1. 
Neuroptera: Myrmeleon, 3. 
Megaloptera: Sialis, 1. 
Isoptera: Termes, 1. 
Orthoptera: Gryllus, 1; Ceuthophilus, 1; Locusta, 1; Melanoplus, 1; Dissosteira, 1. 
Crustacea: Cambarus, 36; Hyalella, 2; Plankton, 1; Daphnia, 2; Microcystis, 1; 
Limnocalanus, 1. 
Arachnida: Argiope, 1; Phaleana, 1; Spiders, 1. 
Myriapoda: Centipeds, 1; millipeds, 1. 
Annulata: Lumbricus, 1. 
Mollusca: Snails, 5; slugs, 2. 
Nemathelminthes: Ascaris, 1. 
Protozoa: Volvox, 1. 
Chordata: Snake blood, 1; human blood, 1; mouse, 1. 
All of these, except human blood, reacted positively for copper, 
showing varying amounts. 
As a final phase, the sources of copper were studied. Some 30 
incinerations were made of twelve species of plants, all of which showed 
traces of copper. The soil and: water were also tested, with positive 
results. 
All of the Arthropoda studied showed a surprising uniformity in 
their reactions for copper. In practically all cases copper was present 
in quantities nearly equal to that of crayfish blood. This uniformity 
must have its significance. Copper in the quantities found could not 
come to the insects in their daily feeding, unless the tissues exercised a 
discriminating selection for the copper in their food. This copper 
must be functional, and because of the analogies pointed out it is inter- 
preted as forming the nucleus of a respiratory protein, hemocyanin. 
There is a further point to be considered. Unless we assume a 
blood protein to fix the oxygen, we cannot account for the presence of 
oxygen in the blood of insects living under practically anaerobic con- 
ditions, that is, insects living in warm and stagnant water. 
Physically, oxygen tends to form a balance on both sides of a moist 
or immersed membrane. But since in the summer there are two 
factors which tend to decrease the oxygen supply available to insects 
in the water, namely organic decomposition and the heat of the water, 
the amount of oxygen, on a purely physical basis, would diminish also 
within the insect. Water contains its largest amount of dissolved 
oxygen at zero, and as the temperature rises this amount becomes less 
