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red. Henle, in his original memoir on this genus, says that 
the fluid in mass has a rosy tint. Some Oligochaeta have a 
very much, smaller per-centage of Haemoglobin in their vascu- 
lar fluid than others. 
It is noteworthy, as bearing on the function of Haemoglobin 
as evidence from comparative physiology, that those Inverte- 
brata in which this body is markedly present, occurring as 
an exception or in unusual quantity, are forms living in the 
foulest mud, in water sometimes almost destitute of dissolved 
oxygen, and in which sulphuretted hydrogen and carbonic 
acid occur in excess. The Haemoglobin enables them to seize 
what little oxygen there is. Plunorbis corneus (an air- 
breather truly) lives in very foul pools; the larva of Chiro- 
nomus lives in black foetid slime in ponds ; so do many of the 
Limicolous Oligochaeta. Branchipus occurs in ponds which 
are destitute of vegetation, and are more mud than water; it 
has for companions in the pond on Blackheath Chironomus- 
larvce and a few Oligochaeta, besides minute Entomostraea. 
I take this opportunity of pointing out that Preyer’s pro- 
posed estimation of the exact amount of Haemoglobin in a 
solution by the spectroscope is not a practicable thing, since 
the definition of a band of absorption, with given strength 
and thickness of solution, must depend on the spectroscope 
used, some having much better definition than others. 
Besides this, the personal error must come in very largely in 
such a method. 
Standard for Spectroscopy. — There is a great want of 
some common and natural standard to which to refer 
absorption spectra in description. Many valuable observa- 
tions are lost for want of such a standard, and others 
are misunderstood. The solar lines are not suitable for 
various reasons. Mr. Sorby has proposed a quartz plate 
of given thickness and Nicol’s prisms, but it is very 
difficult to get this apparatus exactly made. I venture 
to propose the red fumes or gas known as nitrogen tetroxide 
(N 2 0 4 ). This gas, sealed in a small tube, furnishes an ex- 
cellent standard by which I hope hereafter to describe absorp- 
tion spectra. There is no difficulty whatever in obtaining or 
keeping it, and I hope that it may become a general thing to 
state what relations any bands observed in the spectrum of a 
new or important body have to those given by nitrogen 
tetroxide. 
The details as to the action of “ ozonic ether” on the blood 
of Invertebrata and on blood products, as also details as to 
Haemoglobin, Chlorocruorin, and Chlorophyl in Invertebrata, 
