42 DEVELOPMENT OF RED BLOOD-CORPUSCLES. 



ular-filamentous transformation of the previous nucleus. This body, designated 

 nucleoid, is surrounded by a zone of paraplasm, enclosing hemoglobin and gran- 

 ular and hyaline matter "in a filamentous framework. Nucleoid and paraplasm 

 may under certain conditions be extruded from the erythrocytes. Perhaps these 

 contribute to the formation of blood-plates. 



B. Development of Vessels and Blood-corpuscles in the Earliest Pest- 

 embryonal Period. Following J. Arnold, Golubew believes that the 

 blood - capillaries present in the tail of frog -larvae form in various 

 situations at first solid buds that grow more and more deeply into the 

 tissues, enter into anastomotic union with adjacent buds and finally 

 become hollow, with disappearance of their protoplasmic contents. 

 The capillaries would thus like an intricate branched network make 

 their way into the tissues and spread like a foreign intruder. Ranvier 

 observed the same process of growth in the omen turn of newborn cats. 

 The development of the capillaries and at the same time of the blood- 

 corpuscles in their interior has been observed in an especially instruc- 

 tive manner in the large omentum of the young rabbit. .When a 



week old, the omentum in 

 these animals exhibits dull- 

 white spots in whose in- 

 terior lie so-called vessel- 

 forming or vaso-formative 

 cells (Fig. 5), that is, 

 strongly refracting cellular 

 elements varying widely in 

 shape, and provided with 

 protoplasmic processes (a). 

 The protoplasm of these 

 cells resembles that of the 

 lymph-cells, particularly 

 with respect to its mark- 



FlG. 5. Formation of Red Blood-corpuscles within "Vaso-forma- ^^1 1 Tr rp.ft-a r>-rin cr r>li a t-a r>t Ar 



five Cells," from the Omentum of a Rabbit Seven Days Old: 

 r, r, the formed corpuscles; K, K, nuclei of the yaso-forma- in the interior OI these 



capuiariis."' a> pr cesses which ultimatdy unite to form cellular structures can be 



seen rod-shaped nuclei ar- 

 ranged longitudinally (K K) and red blood-corpuscles (r r), both sur- 

 rounded by protoplasm. From the vessel-forming cells protoplasmic 

 shoots and processes arise, which in part terminate free and in part 

 unite to form a delicate network. In some places nucleated connec- 

 tive-tissue corpuscles arranged longitudinally lie upon the structures. 

 These constitute the beginning of the connective-tissue perivascular 

 sheath. 



The vessel - forming cells appear in various shapes, either longi- 

 tudinally cylindrical, with pointed extremities, or round or oval, rather 

 resembling large lymph -cells or connective-tissue cells. These cells 

 are always the seat of origin of non-nucleated erythrocytes, which thus 

 arise in the protoplasm of the vessel-forming cells, as the chlorophyl- 

 grains or starch-granules arise in the protoplasm of vegetable cells. 

 Only after the blood-corpuscles have thus formed within their interior 

 do these cells unite through their processes with the vascular system. 

 Their tubular arrangement becomes connected with adjacent vessels 

 and the blood-corpuscles are washed away. In rabbits from four to 

 six weeks old these areas contain fewer and fewer corpuscles. If it be 



