bodies; the multinucleate cell, 10, has both; cell 

 11, which is similar to 10, has neither. The cell 

 in figure 326 is shown under high magnification 

 to reveal the orange bodies in greater detail. 

 These characters are present in some cells, and 

 are absent from others. This is true not only in 

 the embi-yo but also in the adult bone marrow 

 (figs. 398 and 399) . Regardless of these varia- 

 tions the bone marrow of the bird contains but a 

 single type of giant cell, the osteoclast, whereas 

 in mammalian bone marrow there are two types — 

 the one just mentioned and the megakaryocyte, 

 which produces platelets. Nucleoli found in the 

 binucleate and mononucleate stages of develop- 

 ment are still retained in the nuclei of the fully 

 differentiated osteoclasts of bone marrow from 

 adult birds. 



A conspicuous nucleolus, characteristic of tlie 

 osteoclast, may be found also in tissue culture of 

 tliis cell (Hancox, 1946). This author ex- 

 pressed the opinion that the nniltinucleated con- 

 dition of this type of giant cell arose by a fusion 

 of cells, rather than by multiple division of a nu- 

 cleus within a single cell. 



The cytoplasm of some multinucleate osteo- 

 clasts contains magenta-colored bodies. Some 

 of these bodies have irregular shapes; some, like 

 the example in cell 4, of figure 320, are spher- 

 ical; and some — see those between cells 12 and 

 14 of figure 320 — are masses of stainable sub- 

 stance without definite form. 



A series of mononuclear osteoclasts have been 

 drawn under high power in order to give a closer 

 view of this substance. Figure 326 is a young 

 osteoclast showing the characteristic vacuoliza- 

 tion of the cytoplasm, but without magenta- 

 colored strands. In figure 324 a slight amount 

 of this material exists in the form of cui-ved bars 

 concentric to the vacuole walls. Two spheres 

 are shown in the lower tip of figure 327; the 

 magenta bodies contained within them are not as 

 definitely an integral part of the cell as are the 

 cui-ved bars in figure 324. A rather extreme 

 condition is shown in figure 328, where many 

 vacuoles contain many, twisted threads of this 

 substance, but more important is the fact that 

 at the left side of the cell this substance appears 

 to be undergoing a transition to the typical orange 

 masses characteristic of osteoclasts generally. 



The magenta substance seemed to have a pre- 

 dilection for osteoclasts even in the early stages 

 (cell 15, fig. 320). This was not always the 



case, however, and other cell types might show 

 vacuoles with colored strands of this type. These 

 magenta masses did not appear in sectioned ma- 

 terial, which suggested that they are artifacts but 

 did not prove it. 



Sometimes magenta masses occur in the senmi 

 outside the osteoclasts. Since they appear to 

 merge with the serum, it is possible that serum 

 condensations on the cells at the time the slide 

 is made could account for all these irregular 

 magenta-stained bodies but certainly this is not a 

 convincing conclusion at present. 



Another possibility considered was that this 

 substance represented a dissolved cartilaginous 

 matrix taken up by the osteoclasts, or that cells 

 containing this substance represented hypertro- 

 phied and degenerating cartilage cells liberated 

 into the expanding marrow cavity. Cartilage at 

 the end of the femur was pressed hard against 

 the slide in making the smears but no cells were 

 found with a morphology that would support the 

 idea that magenta-colored masses and strands 

 arose from cartilage cells. In fact no evidence 

 was obtained by the smear method that cartilage 

 cells were liberated into the marrow cavity after 

 the cartilage was dissolved. By the section 

 method, Dantschakoff (1909b) observed that 

 viable cartilage cells survived after the lacunae 

 broke down. She stated (p. 874) : 



"Die Knorpelzellen, die dabei aus ihren Kap- 

 seln befreit werden, bieten besonders bei dem 

 ersten Auftreten der Markliohle keinerlei An- 

 zeichen von Degeneration. Sie bleiben als runde 

 helle Zellen zwischen den Elementen des von aus- 

 sen eindringenden Mesenchymgewebes liegen. 

 Einige von ihnen, die dem Rande der Hohle un- 

 mittelbar anliegen, zeigen sogar im Gegenteil 

 mitotische Teilungsfiguren. ..." * 



Concerning their later history, she says (p. 

 882): 



". . . Die aus den Kapseln befreiten Knorpel- 

 zellen vermischen sich in der engsten Weise mit 

 den Elementen des in dasselbe Gebiet eindringen- 

 den jungen Mesenchyms. Bei ihrer allmah- 

 lichen Entfernung von der Knorpelgrenze schei- 

 nen sie sich zu strecken und Auslaufer zu bilden. 



■* Translation : The cartilage cells which thus become free of 

 their capsule do not give any sign of degeneration especially 

 at the first emergence of the marrow cavity. They persist as 

 round clear cells among the elements of the mesenchyme tissue 

 that is penetrating from the outside. On the contrary, some 

 of them, lying right against the edge of the hollow, exhibit 

 mitotic division forms. 



153 



