SOME OF THE WAYS IN WHICH ANIMALS BREATHE. 311 
with hemoglobin, the reduced solution has only to be shaken up 
with air for the two bands characteristic of oxy-chlorocruorin to 
reappear. 
The fact that the blood of some snails is blue has been known 
for nearly fifty years, and since 1817 various corroborating 
observations have been reported; it remained, however, for a 
Belgian observer, M. Frédéricq, to put our knowledge on a firm 
foundation. In 1878 he described the phenomena presented by 
the blood of the Octopus; he found it to be blue on exposure to 
air, but to lose its colour when boiled in the receiver of an air- 
pump, or when reduced by the passage through it of a current 
of carbonic acid or of sulphuretted hydrogen ; so far it resembles 
hemoglobin, to which also it is similar in being composed of a 
proteid body, and of another which contains a mineral ; this 
mineral, however, is copper, and not, as with hemoglobin, iron. 
Frédéricq reported that oxy-hemocyanin has no absorption- 
bands, but Dr. Halliburton finds that with an oxidised solution 
the ends of the spectrum are cut off, while there is no such 
diminution of light with a reduced solution. 
Hemocyanin is not confined to Octopus; it has been found 
by Krukenberg in the blood of the Sepia and the Squid, of the 
ear-shell (Haliotis), Murex (the purple snail of the Romans), 
and other Gastropods ; by the same physiologist in the Crayfish 
and the Crab, and other Crustacea; and by Frédéricq in the 
Lobster. Professor Ray Lankester, as he doubtless told in an 
earlier lecture of this course, found it both in Limulus and in 
the Scorpion. 
With regard, then, to the mode of respiration which is com- 
parable to our own storing up of oxygen in the red blood 
corpuscles, and giving it to the oxygen-carrier hemoglobin to 
distribute through the body, we find that all normal Vertebrates 
(here, of course, the Lancelet is not included) do the same; so 
do two molluscs, five worms, and one holothurian. A number 
of worms, some molluscs, some Echinoderms, and two Crustacea 
are known to have hemoglobin dissolved in their blood ; others 
have instead a green or a blue colouring matter, which in all the 
essential particulars of a respiratory colouring matter resemble 
hemoglobin. Four Crustacea have tetronerythrin in their 
_ blood, and some Lepidoptera have chlorophyll. Here we have 
colouring matters in the blood. Incidentally I have told you 
