1890-91.] AMPHIBIA BLOOD SlUDIES. 257 



presence of a few haematoblasts like those shown in Figs, lo and ii 

 in the channel of the branch of the mesenteric artery. 



As I have never found in adult caudate Amphibia haematoblasts in any- 

 other organ than the spleen and then only in its blood sinuses, these 

 may be regarded as direct descendants of the haematoblasts which arise 

 by proliferation of the cells of the ventral portion of the visceral 

 plate of the mesoblast. 



It is, I think, worthy of note that though there is but one source for 

 all haematoblasts, yet there are two stages in their history, the second of 

 which appears when the liver begins to take on its adult structure, the 

 forms belonging to this stage being remarkable for their great capacity 

 for division, while the first series of haematoblasts are, almost wholly, 

 formed in the subintestinal veins and the great majority of them 

 are directly converted into red cells, the remainder persisting to form the 

 haematoblasts of the second stage. 



IV. Conclusions. 



1. The haemoglobin of the blood corpuscles is derived from the abun- 

 dant nuclear chromatin of the haematoblast. 



2. The fusiform cells of Amphibian blood are derived from the red 

 corpuscles, the latter in this conversion losing the cell membrane and the 

 greater portion of the discoplasma. 



3. The haematoblasts in Amblystouia are direct descendants of cells 

 split off from the extreme ventral portions of the visceral mesoblast and 

 they pass, at first, a portion of their existence in a specialized part 

 of the original body cavity of the embryo. 



V. Appendix.* 



The foregoing paper was written, part in 1889, part in 1890. The 

 publication of it now seems opportune since one of the conclusions con- 

 tained in it has been fully confirmed by the results of m\' investigations 

 during the last year. The cJiromatin of every cell, animal and vegetable, is 

 an iron compound and this can be proved not only by the use of freshly 

 prepared ammonium sulphide, as described in a communication sent to 

 the Royal Society of London f last year, but also by other methods since 

 discovered, the use of which excludes inorganic and albuminate iron and, 

 at the same time, does not affect the iron in haemoglobin or haematin. 

 With the more recently discovered methods, so easy is their application 



* Written Feb. 4, 1892. 



t Proceedings, Roy. Soc, Vol. 50, p. 277. 



