70 Ossification Process in Birds, &c. By Br. L. Schoney. 
with ; and secondly, these, when they are first formed, have as yet 
no connection with the old blood-vessels. 
The transformation of cartilage into marrow elements is visible 
in Fig. 4. The limeless zone of the cartilage {a) is suddenly 
replaced by a protoplasm, in which are interspersed numerous 
lustrous small particles. The latter generally appear surrounded 
by a small bright margin, through which, with careful illumination, 
are seen small trabeculse, which, on account of their lustre and 
homogeneous structure, remind us of one of the formations in 
mammals described as " hamatoblasts. Sections such as those 
rendered in the drawing, force us so to say to the supposition that 
not only the cartilage corpuscles, but the whole living matter, 
which is gathered in the interior of the cartilage elementary sub- 
stance, participate in the marrow formation. The sudden transition 
from apparently structureless elementary substance to a free proto- 
plasm layer, without the least indication of division of the cartilage 
corpuscles, would scarcely admit of any other explanation. 
Frequently there are found in the solution border of the 
elementary cartilage substance, cartilage corpuscles, which partly 
are placed in the same, and partly already reach into the first-formed 
marrow-space, and never have I observed in such corpuscles any 
division whatever. If people, notwithstanding the idea of division 
of the cartilage cells," adduce as proof two close- together-lying 
elements, or elements with two or more nuclei, they simply forget 
that the hard elementary substance does not admit of enlargement 
of the elements, which surely ought to precede the simple divi- 
sion. The latter will certainly have first to be secreted before 
the protoplasm can show signs of life to a full extent; and to 
me the supposition appears to be more in accordance with the fact 
of the matter, that a new formation of living material takes place in 
certain centres of the just freed protoplasma (even thus conducing 
to the formation of the compact lustrous small particles), than the 
clinging to the diagramatic " cells-partition theory," which certainly 
no facts justify. The so frequently visible multinuclear proto- 
plasm bodies (Myeloplaxa) will according to this view have simply 
to be considered as freed cartilage-tissue units (territories), and we 
very easily understand that sometimes a number of such units are 
secreted to a large common protoplasm layer before further changes 
take place in the latter. 
So much appears to me to be out of the question, that in birds, 
just as in mammals, cartilage tissue becomes direct marrow tissue. 
The next question then will be : How is bone tissue formed out of 
marrow tissue ? This question too has had many different answers. 
The progress in our knowledge of the histogenesis, however, is not 
less visible here than in other tissue-fields. 
Gegenbaur was the first who considered the " osteoblast " as 
