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XIX.—On the Histology of the Blood of the Larva of Lepidosiren paradoxa. 
Part I]. Hematogenesis. By Thomas H. Bryce, M.A., M.D. (With Four Plates.) 
(Read July 18, 1904; MS. received October 15, 1904. Issued separately May 6, 1905.) 
INTRODUCTION. 
In the first part of this memoir I described the structure of the corpuscles at a 
stage of larval development when the red cells were actively dividing and the blood 
contained several varieties of white cells. During the course of these more strictly 
eytological observations, it was impressed upon me that the great size of the elements 
and their very marked histological characters, combined with the simple character of 
the organisation of the animal, made Lepidosiren a very favourable case for the study 
of the first principles of Hzematogenesis. I was specially interested in what may be 
termed a middle phase in the history of the blood. I refer to a period after the primi- 
tive corpuscles have acquired hemoglobin and there are leucocytes present, but before 
the blood-forming organs are unfolded. This stage lasts a relatively long time in 
Lepidosuren up to the differentiation of the spleen, as the liver takes no part in blood- 
formation at any period. 
Since Bizzozero first discovered that heemoglobin-containing cells divide by mitosis, 
and emitted the hypothesis that the red cells are a stirp kept up only by division, it 
has been largely held that all forms of the coloured corpuscles are descendants of those 
first laid down. 
The admission of a non-hemoglobin-containing element into the erythrocyte series 
(Lowir and Denys) only pushed back the argument from the ‘hematoblast’ of 
_ Neumann to the ‘erythroblast? of Lowir. If the erythrocyte series constitutes a 
“tissue ’ su generis, when does it cease to be laid down ? 
We know from observations on the characters of the corpuscles at various stages of 
development that in all vertebrates the elements are at first identical, but that their 
characters change, and the adult corpuscles are different in character from those which 
first appear. It is sometimes assumed that the adult nucleated erythrocytes of the 
lower vertebrates correspond to the nucleated discs of mammals, but in the Lepidosiren 
larva the erythrocyte series shows all the stages seen in the higher forms. There 
are ‘erythroblasts’ without hemoglobin; ‘hzmatoblasts’ with hemoglobin; young 
erythrocytes with reticular nucleus; and mature or old forms with vesicular nuclei. 
All forms save the last divide by mitosis, and the last is probably only a hemoglobin 
carrier like the mammalian red blood corpuscles.* Thus, though the outward form of 
* Of. Laaunsse, Journal de lV Anat., T. 26, 1890. 
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