ORIGIN OF THE RED BLOOD-CORPUSCLES. 13 



coloured, retain their nucleus, and are capable of undergoing multipli- 

 cation by division ; and, in fact, Remak observed all the stages of the 

 process of division. The process of division is best seen from the 3rd 

 5th day of incubation. Increase by division also takes place in the 

 larvre of the salamander, triton, and toad (Flemming, Peremeschko). 



After the liver is developed, blood-corpuscles seem to be formed in it 

 (E. H. Weber, Kolliker). Protoplasmic, nucleated, colourless cells are 

 carried by the vena porta from the spleen into the liver, where they 

 take up pigment. Neumann found in the liver of the embryo proto- 

 plasmic cells containing red blood-corpuscles. The spleen is also 

 regarded as a centre of their formation, but this seems to be the case 

 only during embryonic life (Neumann). Here the red corpuscles are 

 said to arise from yellow, round, nucleated cells, which represent 

 transition forms. Foa and Salvioli found red corpuscles forming 

 endogenously within large protoplasmic cells in lymphatic glands. In 

 the later period of embryonic life, the characteristic non-nucleated 

 corpuscles seem to be developed from the nucleated corpuscles. The 

 nucleus becomes smaller and smaller, breaks up, and gradually dis- 

 appears. In the human embryo at the fourth week only nucleated 

 corpuscles are found ; at the third month their number is still }-|- of 

 the total corpuscles, while at the end of fetal life nucleated blood- 

 corpuscles are very rarely found. Of course, in animals with nucleated 

 blood-corpuscles, the nucleus of the embryonic blood-corpuscles remains. 



(B.) Development of Blood-Vessels, Formation of Blood- Vessels and 

 Blood-Corpuscles during Post-embryonic Life. Kolliker assumed 

 that, in the tail of the tadpole, capillaries are formed by the anasto- 

 moses of the processes of branched and radiating connective tissue- 

 corpuscles. These corpuscles lose their nuclei and protoplasm, become 

 hollowed out, join with neighbouring capillaries, and thus form new 

 blood-channels. Von Golubew, on the other hand, opposes this view. 

 He assumes that the blood capillaries in the tail of the tadpole give off 

 solid buds at different places, which grow more and more into the 

 surrounding tissues, and anastomose with each other ; their protoplasm 

 and contents disappearing, they become hollow and a branched 

 system of capillaries is formed in the tissues. Eanvier, be it remarked, 

 noticed the same mode of growth in the omentum of newly-born 

 kittens. 



The latter observer has recently studied the development of blood- 

 vessels and blood-corpuscles in the omentum of young rabbits. These 

 animals, when a week old, have, in their omentum, little white or 

 milk spots (" taches laiteiises," Ranvier), in which lie " vaso-formative " 

 cells, i.e., highly refractive cells of variable shape, with long cylindrical 

 protoplasmic processes (Fig. 5). In its refractive power the protoplasm 



