332 
PROFESSOR POUCHET. 
to hypotheses. It is upon this obscure problem that I wish 
to throw some light. 
One need only look back over the last two years of the 
morphological study of the blood^ to see how many organs 
have been put forward, one after another, as the birthplaces 
of the corpuscles, both white and red. 
Theories and hypotheses have not been wanting ; the 
lymphatic glands, the spleen, the marrow of the bones, and 
other organs, have been looked upon as the seat of origin 
of the formed elements of the blood, and even called, on that 
account, " haematopoietic organs.” It must be allowed that 
the question of haematogenesis is far from being a simple 
one, and that among various animals it presents itself under 
very different aspects. 
We may recognise, in the first place, two great classes : 
Firstly. — Oviparous animals, either warm- or cold- 
blooded, in which the haematids possess a nucleus. 
Secondly. — Mammals, in which the haematids, although 
at first like those of oviparous animals, are replaced at a 
very early stage by corpuscles, absolutely devoid of a 
nucleus. 
If one considers all animals with regard to their haema- 
topoietic organs, it is evident that many animals have neither 
marrow nor lymphatic glands, e.g. fishes. 
In the same way there are some in which the spleen is 
quite rudimentary (Syngnathus), or even entirely wanting 
(Lampreys). 
Among mammals, even the Rodents, in which the vascular 
area persists and forms blood- corpuscles at a very late period ; 
and, on the other hand, the Marsupials, in which the umbilical 
vesicle has disappeared, even before any part of the primor- 
dial skeleton has become vascular, offer various points which 
call for special attention. 
In order to solve the problem of hsematogenesis, we want 
to obtain a large number of data which would be useful 
to us. 
By what certain characteristics can we recognise those 
elements which are newly formed from those which are 
about to degenerate? How long do they live ? For it is 
impossible to admit the long life of elements, the regeneration 
of which is so easy after lesions, and even in the normal state 
of things in woman between puberty and the critical age. 
The more or less satisfactory answers to all these ques- 
tions, which have been made by recent research, I wish to 
1 ‘ Gazette Miidicftle/ Nov. 10th, 1877 i Jan. 19tii, Feb. 2nd, March 
10th, April 27th, 1878 i and ‘Journal dc i'Anatomie,* Jaw,, 1879. 
