ITS PHYSICAL, CHEMICAL, AND STRUCTURAL CHARACTERS. 251 



of former observers) to be the concurrent opinion of nearly all who have in 

 recent times specially devoted themselves to this inquiry. The first Jvrd 

 corpuscles unquestionably have their origin, like the original cells of the 

 solid tissues, in the primordial cells of the germinal structure; and it is in 

 the "mesoblast" or so-called "vascular layer" of the "blastodermic vesicle" 

 (chap, xviii, sect. 4), and the mass of cells which constitute the rudiment 

 of the heart, that this metamorphosis seems first to take place. The situa- 

 tion of the heart, and the course of the principal trunks of the " vascular 

 area," are early marked out, by the peculiar disposition of the aggregations 

 of cells from which these organs are to be developed; and whilst the outer 

 portions of these aggregations are transformed into the walls of the respec- 

 tive cavities, the inner portions seem partly to deliquesce, and partly to re- 

 main as isolated cells floating in the liquid thus produced. These isolated 

 cells are the first blood-corpuscles; and the following account of them in the 

 Oviparous Vertebrata or Pyrensemata is given by Foster and Balfour, 1 and 

 differs but slightly from that by Klein. 2 In the pellucid area, where the forma- 

 tion of bloodvessels may be most easily observed, a number of mesoblastic 

 cells are seen to send out processes which unite and form a protoplasmic net- 

 work, with nuclei at the points from which the process started. The nuclei, 

 which as a rule are much elongated and contain large oval uucleoli, increase 

 very rapidly by division, and form groups at the nodal points. The ma- 

 jority of these acquire a red color and become converted into blood-corpus- 

 cles, but a few, generally on the outside of the group, remain unaltered. 

 The protoplasm in which the central reddened nuclei are imbedded becomes 

 liquefied, whilst that on the outside of each group as well as that of the unit- 

 ing processes remains granular and forms an investment for the unaltered 

 nuclei which are imbedded in it, Each nodal point is thus transformed 

 into a more or less rounded mass of blood-corpuscles floating in plasma, but 

 enveloped by a layer of nucleated protoplasm, the several groups being 

 united by strands of nucleated protoplasm. By the growth of the strands 

 and the transformation of nuclei in their interior a series of communicating 

 vessels are formed containing corpuscles which when removed from the 

 vessels exhibit energetic amoeboid movements, and probably increase by 

 division. 3 



183. That after the Chyle and Lymph have begun to flow into the cir- 

 culating current, the continued generation of Red corpuscles is due to the 



1 Elements of Embryology, 1874, p. 69. 



2 Sitz-ber. d. Wien. Akad., 1871, Bd. Ixiii, Abth. ii. For other accounts see Afa- 

 nassieff in idem, Bd. liii, 1866, Goette, Schultze's Archiv, 1873, and His, Neben 

 die Erste Anlage des Wirbelthierleibs. 



3 A different account has lately been given by Dr. H. D. Schmidt, Monthly Micro- 

 scopical Journal, 1874, p. 45, from observations made on a very early human embryo. 

 In this case the young colored corpuscles appeared to be developed in the interior of 

 mother-cells, at the expense of which they grew, and from which they ultimately be- 

 came detached, leaving a dimple at the point of separation. One, two, or three, 

 young corpuscles were sometimes seen in a parent corpuscle, and the young ones 

 themselves sometimes had a third generation in their interior prior to their own 

 escape. This method of increase forms, as Dr. Schmidt observes, the transition from 

 endogenous development to generation. The parent-cells themselves appeared to be 

 derived from the interior primary glandular follicles, formed of hexagonal cells in 

 the walls of the umbilical vesicle," and he is of opinion that the so-called nuclei of 

 the first set of blood-cells are in reality the embryonic red blood-corpuscles which, 

 when first formed, exactly resemble the corpuscles of the adult, except that the cen- 

 tral depression is less distinct. See also Schafer, Proceed. Roy. Soc., xxii, No. 151, 

 who shows that blood-corpuscles arise in the interior of the vacuolated and nucleated 

 cells of connective tissue; the haemoglobin being deposited in the form of minute 

 globules, which increase in size and form the corpuscles, whilst the cells elongating, 

 branching, and uniting with others form the vessels. 



