PROGRESS OF MICROSCOPICAL SCIENCE. 173 



absorption bands, as also in the scales of fish and in the skin and hair 

 of mammals, and in the pigments of many Crustaceans, Annelids, 

 Insects, Tunicates, and Sponges.* 



" From a consideration of the facts stated above with regard to 

 the mode of occurrence and distribution of Haemoglobin in animal 

 organisms, the following general statements may be made, which are 

 in accordance with the now thorough establishment, by chemical 

 investigation, of its peculiar oxygen-carrying property. 



" Hemoglobin is irregularly distributed throughout the animal 

 kingdom, being absent entirely only in the lowest groups.f It may 

 be present in all the representatives of a large group, with but one or 

 two exceptions, or it may be present in one only out of the numerous 

 members of such a group ; or, again, it may be present in one and 

 absent in another species of the same genus. It may occur in cor- 

 puscles in the blood, or diffused in the liquor sanguinis, or in the 

 muscular tissue, or in the nerve-tissue. The same apparent capricious- 

 ness characterizes its occurrence in tissues as in specific forms. It 

 may be present in one small group of muscles and absent from all the 

 rest of the tissues of the body, or it may occur in one part only of a 

 tissue, histologically identical throughout its distribution in the 

 organism. The apparently arbitrary character of this distribution is 

 to be explained (though only partially) by a reference to the chemical 

 activity of Haemoglobin. "Wherever increased facilities for oxidation 

 are requisite, Haemoglobin may make its appearance in response ; 

 where such facilities can be dispensed with, or are otherwise supplied, 

 Haemoglobin may cease to be developed. 



"The Vertebrata and the Annelida possess a blood containing 

 Haemoglobin in correlation with their greater activity as contrasted 

 with the Mollusca, which do not possess such blood. The actively 

 burrowing Solen legumen alone amongst Lamellibranchiate Mollusks, 

 and amongst Gasteropods only Planorbis, respiring the air of stagnant 

 marshes, possess blood containing Haemoglobin. In the former the 

 activity, in the latter the deficiency of respirable gases are correlated 

 with the exceptional development of Haemoglobin. But we cannot 

 as yet offer an explanation of the absence of Haemoglobin from the 

 closely-allied species of Solen, and from the Lymncei which accompany 

 Planorbis. The Crustaceans Clieiroceplialus and Daphnia, and the 

 larva of Gheironomus, possessing, as exceptions in their classes, Haemo- 

 globin in their blood, inhabit stations where the amount of accessible 

 oxygen must be small (that is to say, stagnant ponds), the last living 

 in putrescent mud ; whilst the possession of abundant Haemoglobin in 

 its vascular fluid may be supposed to be one of the chief properties 

 which enables the oligochnst Annelid Tubifex to hold its ground in the 

 foul, and therefore much deoxygenated, water of the Thames at London. 



* See 'Journal of Anatomy and Physiology,' 1869-70, p. 119. 



t [Note. Dec. 24th, 1872.] — It is perhaps of some significance that Haemo- 

 globin Las only been found in that great group of the animal kingdom which in 

 the course of its development gives rise to a middle layer of blastodermic cells or 

 mesoderm, and in examples from nearly every great branch of this stem. 



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