1891-92.] A. B. Griffiths on ilie Blood of the Invertehrata. 123 
and carbonic anhydride are partly dissolved and partly in a state of 
loose chemical combination with certain constituents of the blood. 
The oxygen is united to the haemoglobin, haemerythrin, or chloro- 
cruorin, as the case may be ; and possibly the greater part of the 
carbonic anhydride is united to certain salts contained in the blood. 
Invertebrate blood which contains haemoglobin has a greater 
power of combining with and absorbing oxygen than blood which 
contains either haemerythrin or chlorocruorin. This statement may 
be represented by the following figures, which are the averages of 
the results represented in the previous table : — 
Blood containing hseinerythrin absorbs, &c., . 12*31 percent, of oxygen. 
,, cblorocrnorin ,, .12*48 ,, ,, 
,, bsemoglobin ,, .12*80 ,, ,, 
Although haemerythrin and chlorocruorin are not so active as 
respiratory proteids as haemoglobin, the former are as important as 
the latter. It is probable that by a process of physiological selection 
the respiratory proteids may have become more complex, and their 
molecular instability * therefore greater as the animal body became 
more elaborated, and a necessity arose for the setting apart of 
respiratory proteids for abstraction of oxygen from the air. 
The Blood of Insects. 
In a large number of insects the blood is colourless, although 
sometimes it is of a green, yellow, or red hue. This colour is not 
due to the amoeboid corpuscles, but to the plasma in which they 
float. 
The blood-plasma of Musca domestica (house-fly), f and that of 
the larva of Chironomus | (both belonging to the Diptera)^ contains 
haemoglobin. 
Boulton § has made a number of observations on the blood of 
the Lepidoptera. The colour of the blood in these insects is princi- 
pally green ; but it varies, to a certain extent, with the food. This 
pigment has no respiratory function ; and, in fact, no respiratory 
* For instance, hsemoglobin is less stable than hseniocyanin. See Dr 
Griffiths in Comptes Rendus, t. cxiv. p. 496. 
t MacMunn, Proc. Birmingham Phil. Soc., vol. iii. p. 385. 
t Lankester, Jour. Anal, and Phys., vol. ii. p. 114. 
§ Proc. Roy. Soc. Bond., 1885, p. 270. 
