18 DISTRIBUTION OF HEMOGLOBIN AND ALLIED SUBSTANCES 



Dhe-nS (Compt. rend. soc. biolog., 1903, LV, 1162) records by the colori- 

 metric method, in comparing the bloods of the dog and Planorbis corneus, 

 that the oxygen capacity of the latter is the higher m the dog 1.34 c.c. 

 of per gram (Hiifner) and in Planorbis 1.92 and 2.24 c.c. 



CAUSES OF THE PECULIARITIES IN THE DISTRIBUTION OF 

 RESPIRATORY PIGMENTS. 



The extraordinarily erratic manner in which hemoglobin, hemocyanin, 

 and other respiratory pigments are distributed among invertebrates has 

 not unnaturally given rise to inquiries of the reasons. Ray Lankester 

 (loc. cit.) from such an investigation writes as follows: 



From a consideration of the facts with regard to the mode of occurrence and dis- 

 tribution of hemoglobin in animal organisms, the following general statements may be 

 made, which are in accordance with the now thorough establishment, by chemical inves- 

 tigation, of its peculiar oxygen-carrying property. Hemoglobin is irregularly distrib- 

 uted throughout the animal kingdom, being absent entirely only in the lowest groups.* 

 It may be present in all the representatives of a large group, with but one or two excep- 

 tions, or it may be present in only one 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 corpuscles in the blood, or diffused in the liquor sanguinis, or in the mus- 

 cular tissue, or in the nerve tissue. The same apparent capriciousness 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 hemoglobin. Wherever increased 

 facilities for oxidation are requisite, hemoglobin may make its appearance in response; 

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

 cease to be developed. The Vertebrata and the annelids possess a blood containing 

 hemoglobin 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 molluscs, and amongst gasteropods only Planorbis, respiring the air 

 of stagnant marshes, possess blood containing hemoglobin. In the former the activity, 

 in the latter the deficiency of respirable gases are correlated with the exceptional devel- 

 opment of hemoglobin. But we can not as yet offer an explanation of the absence of 

 hemoglobin from the closely allied species of Solen, and from Limnaei which accom- 

 pany Planorbis. The crustaceans Chirocephahts and Daphnia, and the larva of Chi- 

 ronomus, possessing, as exceptions in their classes, hemoglobin 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 hemoglobin 

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

 the oligochacte annelid Tubifex to hold its ground in the foul, and therefore much deox- 

 ygenated, water of the Thames at London. 



The known chemical properties of hemoglobin furnish a more complete explana- 

 tion of its peculiar distribution in tissues. That it should occur in a circulating fluid 

 which is the medium of respiration is obviously related to those properties. Its occur- 

 rence in the voluntary muscles of the most active of Vertebrata, and in the most active 

 muscles of some others (as in the case of the dorsal-fin muscles of Hippocampus), is 

 equally so; so also its occurrence in the most powerfully acting part of the intestinal 



*It 13 perhaps of some significance that hemoglobin has 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 mosoderm, and in examples from nearly every great branch of this stem. 



