DEVELOPMENT OF RED BLOOD-CORPUSCLES. 41 



corpuscles than herbivora. In goats the blood contains 19,000,000 blood-corpus- 

 cles in the cubic millimeter; in the llama, 13,186,000; in the bull finch, 3,600,000; 

 in the lizard, 1,292,000; in the frog, 408,900; in the proteus, 33,600. During 

 the sleep of winter Vierordt observed the number of blood-corpuscles in the mar- 

 mot diminish from 7,000,000 to 2,000,000 in a cu. mm. 



In invertebrates the blood is generally colorless, with colorless cells. In some 

 invertebrates, for instance the earth-worm, the larva of the large gnat, and others, 

 the plasma is red and contains hemoglobin, but the blood-corpuscles are colorless. 

 Red, violet, brownish, greenish, opalescent blood, with colorless corpuscles (ame- 

 boid cells), is found in some mussels. In the cephalopods and in certain snails 

 and crabs a bluish, globulin-like coloring-matter is present in the blood, containing 

 copper and combining with oxygen, hemocyanin, which is decolorized by a defi- 

 ciency of oxygen. Certain round-worms have a green respiratory pigment, chloro- 

 cruorin, while other animals have a yellow, red, or brown pigment of similar 

 function . 



DEVELOPMENT OF RED BLOOD-CORPUSCLES. 



A. The embryonal development of the blood-corpuscles begins in the 

 chicken as early as the first day. The corpuscles develop in groups 

 within large globules of protoplasm that detach themselves from the 

 walls of the vascular spaces resulting from the apposition of the forma- 

 tive cells. At first they are globular, rough, nucleated, larger than 

 the permanent cells and unpigmented. At a later period they 

 take up the coloring-matter and attain their definite form, with reten- 

 tion of the nucleus. Only when the vessels enter into communication 

 with the heart, are the corpuscles swept away or isolated in groups, 

 and then become set free in the circulation. Remak demonstrated all 

 stages of their multiplication by division. Cells dividing by mitosis 

 are observed most abundantly between the third and the fifth day of 

 incubation, but no longer after their escape. 



Multiplication takes place by division also in the larvae of amphibia, 

 as well as during fetal life in mammals in the spleen, the bone-marrow 

 and the liver, and in the circulating blood. Neumann, further, found 

 in the liver of the embryo, protoplasmic cells descendants of the vas- 

 cular endothelium or of the liver-cells enclosing red blood-corpuscles. 

 Besides, there were found in the liver cells with large nuclei, in part con- 

 taining hemoglobin, in part free from hemoglobin, which divided by 

 mitosis and then, with shrinking of the nucleus, became transformed 

 into definitive blood-corpuscles. Foa and Salvioli observed endogenous 

 formation in the lymphatic glands, in addition to the liver and spleen, 

 also within large protoplasmic cells. The spleen also is considered a 

 seat for the formation of the red blood-corpuscles, though only during 

 embryonal life. Here the red corpuscles are believed to be formed of 

 yellow, round, nucleated cells, representing transitional forms. 



From the embryonal bodies (erythroblasts), always at first nucleated, 

 there result, in the later stages of embryonal life, the characteristically 

 shaped and at the same time non-nucleated corpuscles; the nucleus, 

 together with a portion of the protoplasm, disappearing. In the human 

 embryo only nucleated corpuscles are present in the fourth week. In 

 the third month they constitute only from one-eighth to one-quarter of 

 all the erythrocytes, while at the end of fetal life nucleated corpuscles 

 are found only with great rarity (Fig. 8). 



According to some observers, mammalian erythrocytes contain a nucleus-like 

 central body, which Lavdowsky considers as the remains of nuclear substance. 

 According to J. Arnold, the central body sometimes observed consists of a gran- 



