152 Annals Entomological Society of America [Vol. XIV, 
would, therefore, be minimal. Besides, even in such animals as crayfish, 
where the respiratory protein is known to be hemocyanin and bluish in 
color, when fully oxidized, the blood generally shows no color at all. 
It may be entirely transparent, or a pale to definite blue. Or it might 
be a pink to bright red, depending upon the. amount of non-respiratory 
pigment (Tetronerythrin) present. In insects the blood, if colored at all, 
is bluish or greenish, forming black clots. There are exceptions to this, | 
such as adult Dytiscus, in which the blood is saffron yellow to orange 
in color, although blue to purple in the larvee. This color is not due to 
any respiratory protein, but to non-respiratory pigments, which are 
stored in the blood and elaborated into the external colors of the adult. 
Assuming a respiratory pigment for the moment, there are two 
possibilities—the carrier in question may be either hemoglobin, or 
hemocyanin, or both, as in some mollusks. As far as known to the 
writer, hemocyanin has not been definitely reported for insects, while 
hemoglobin is known only for the Chironomid ‘‘blood-worms.”’ 
A considerable number of experiments were performed in the ensuing 
investigations. These experiments on respiratory proteins in insects 
have been described elsewhere, but since they bear on this discussion, a 
summary of the salient points will be necessary. 
The problem as studied, presented the following phases: (1) 
Considering that conditions as met in aquatic insects postulate the 
presence of a respiratory protein, can such a protein be demonstrated ? 
(2) If present, what is its nature? (3) Is it confined to aquatic insects 
possessing blood gills, or is it universal among insects? 
For the first of these it was shown that the blood of insects reacts 
with the oxidation tests for hemoglobin (Guiac, O-tolidin, Benzidine), 
regardless of the species. Only Chironomid blood reacted with the 
hemin tests for hemoglobin. These tests showed that a respiratory 
protein was present. 
In the second phase, considering the nature of this protein, two 
possibilities offered themselves. Of known proteins in Arthropoda, 
there are only hemocyanin and hemoglobin. The first of these has a 
copper nucleus, the second is an iron compound. The hemin tests for 
hemoglobin showed that this protein is restricted to Chironomid “ blood- 
worms” among the insects. It is a fact, however, that the blood of 
Aeshna, Anax, Dytiscus, and other insects showed isolated crystals 
resembling the hemin prisms. If present at all, therefore, hemoglobin 
is available only in infinitesimal quantities and may be disregarded. 
For hemocyanin no direct tests are known. It was held, however, 
that if by some means copper could be shown to be present in insect 
blood in quantities as large as found in crayfish blood where the copper 
has a known function, then its role in both is identical. For this purpose 
a number of incinerations of insect and crayfish blood were made and 
the ashes tested for copper. Both reacted positively, showing copper 
in approximately equal amounts. It was therefore concluded that 
insects contain a respiratory of a nature similar to that of the crayfish, 
namely a hemocyanin. 
