. The structure and life of birds . illlie on a space of one square inch. Among birds theCassowary has the largest, the Humming Bird thesmallest. The colourless ones also are always ex-tremely small, though they vary much in size. Inshape the red ones, seen under the microscope, are,in birds and reptiles, oval ; in man, round. Andthe shape is not the only difference. In birds, reptiles,and fishes there is. a nucleus, a small roundish body inthe middle. In mammals, except in the case of em-bryos, no sign of this is, as a rule, to be found. Whythis nucleus has disappeared, no one has been able t
. The structure and life of birds . illlie on a space of one square inch. Among birds theCassowary has the largest, the Humming Bird thesmallest. The colourless ones also are always ex-tremely small, though they vary much in size. Inshape the red ones, seen under the microscope, are,in birds and reptiles, oval ; in man, round. Andthe shape is not the only difference. In birds, reptiles,and fishes there is. a nucleus, a small roundish body inthe middle. In mammals, except in the case of em-bryos, no sign of this is, as a rule, to be found. Whythis nucleus has disappeared, no one has been able toshow. It certainly cannot be maintained that thereis any superior vitality which we can associate with its VI FORM AND FUNCTION 75 disappearance. It is easy to connect the reptiles lowtemperature with his poverty in corpuscles. The white blood corpuscle is an object of extremeinterest. It is simply a cell of granular appearancewith a nucleus. In shape it is roundish, but whenalive it is a perfect Proteus. If a drop of blood be b c. Fig 22.—(«) and (b) White and red corpuscles of man from Quain after Schafer: (c)and (J) red corpuscles of Humming Bird and Ostrich after Gulliver; (*) Amoebaafter Moore. All to same scale. taken from the finger and put under the microscopethe white corpuscles are easy to make out, scatteredin comparatively small numbers among the red, but,unfortunately, they have ceased to move, the changeof temperature, and conditions generally, havingkilled them. But there are one-celled creatures tobe found in stagnant water which closely resemble 76 THE STRUCTURE AND LIFE OF BIRDS chap. them. These are called Amoebae from their incessantrestlessness. At one moment they may be round,the next they throw out a limb on one side, the nextthat limb is withdrawn and another thrown out else-where. Wherever food comes in contact with themthey make a mouth and swallow it. The colourlesscorpuscle is one of these simplest of creatures, lead-ing a life of its own within
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