No. I.] BLOOD CORPUSCLES. 



103 



though the sketches made (see Fig.) seem to indicate that such 

 movements occur. The figure shows, indeed, that the cor- 

 puscle as well as the nucleus undergoes changes in shape; but 

 this was caused in part at least by the rolling of the cell so as 

 to present different surfaces in successive drawings. A priori, 

 it seems much more likely that the extrusion should result 

 from some active movement on the part of the nucleus rather 

 than from contractile changes in the cell substance. For it 

 seems to be generally admitted now that in certain cells — 

 lymph cells especially (Arnojd) — not only movements of the 

 nucleus may take place, but movements of the granules and 

 filaments in the nucleus. After the escape of the nucleus, the 

 spherical red corpuscle eventually becomes a biconcave disc 

 I have not attempted to follow this change, though I feel con- 

 vinced that the bell shape which Rindfleisch ascribes to the 

 corpuscles which have just lost their nuclei is a mistake. The 

 red corpuscles even of the circulation, as is well known, fre- 

 quently take this shape when treated with reagents of any kind, 

 or even when examined without the addition of any liquid. It 

 seems to me very natural to suppose that the biconcavity of 

 the mammalian corpuscle is directly caused by the loss of the 

 nucleus from its interior. Certainly as long as the corpuscles 

 in the foetus and the adult retain their nuclei, they remain 

 more or less spherical, and after they lose their nuclei they 

 become biconcave. The mechanical conditions of the circu- 

 lation undoubtedly have some influence upon this change, but 

 the initial cause lies apparently in the migration of the nuclear 

 mass from the middle of the cell, so that the viscous material 

 of the corpuscle is permitted to sink in. The biconcavity is of 

 course a decided physiological advantage, as the absorptive 

 surface is thereby considerably increased, so that upon the 

 doctrine of natural selection, one can readily understand why 

 such a variation should have become permanently established. 

 Among the Camellidae, it is true, we have biconvex non-nu- 

 cleated corpuscles. So far as I know, no one has investigated 

 the haematopoietic function in these animals, but it is possible 

 that small spherical erythroblasts are not formed in them as in 

 the other mammalia. 



If we grant that the nucleated red corpuscle loses its nucleus 

 by extrusion when it passes to the non-nucleated form, then 



