320 LESLIE B. AREY 



Jackson ('04) described and figured osteoclasts, which by the 

 enlargement and confluence of cytoplasmic vacuoles formed 

 detached cells; these remain interconnected by processes and 

 are indistinguishable from neighboring reticulum cells. 



The view of Maximow ('10) differs from that of Jackson in 

 that some osteoclasts are said to be destroyed through extreme 

 degeneration. 



Lewis ('13) holds these polykaryocytes to be degenerating 

 cells produced by those conditions which lead to the dissolution 

 of bone. 



Thus, these opinions pertaining to the fate of osteoclasts 

 either uphold their transformation into other cellular elements, 

 their total destruction, or admit both possibilities. 



Several provisional communications by the writer on the 

 problem of the origin, growth, fate and significance of the giant- 

 cells of bone have appeared previously ('17a; '17b; '08) . 6 



MATERIAL 



The observations recorded in this communication have been 

 made on developing membrane bone of human and pig embryos. 

 A favorable site for study is found about the walls of the dental 



6 A publication by Jordan ('18) some time after the present paper had left my 

 hands necessitates supplementary comment. Jordan states (p. 248) that "The 

 osteoclast arises chiefly (at first exclusively) from the marrow reticulum by a fu- 

 sion process essentially as previously described by Maximow; in the earliest 

 stages the nuclei may multiply slightly by mitosis; their increase, however, is 

 due mainly to exogenous additions either reticular, osteoblastic, or even bone 

 cells. Smaller osteoclasts may fuse to form larger syncytia. These cells finally 

 degenerate, as evidenced chiefly by a vacuolization of their cytoplasm and a 

 karyorrhexis, and eventually they disintegrate. The above-described material 

 gives no evidences of a retransformation into marrow reticulum, as maintained 



by certain workers (Jackson, Arey) Osteoclasts may arise to some 



extent also from fusing osteoblasts, .... But the osteoblasts involved 

 in this process are not "worn out" as Arey maintains. On the contrary, they are 

 of the less differentiated types and strongly basophilic." 



As to sources of origin, method of growth, and ultimate fate these conclusions 

 are in harmony with my own, as set forth in former communications ('17 a, '17 b; 

 '18) and in the present contribution. In certain details, however, our opinions 

 diverge widely. The method of osteoclastic origin from marrow reticulum he 

 considers chief in importance, that from osteoblasts secondary; on the contrary, 



