ENDOGENOUS CELL-FORMATION. BROOD-CAVITIES. 443 



originally single cell. But long before this simple view 

 of the process of the cleavage in the yolk had been 

 arrived at, it had been very distinctly perceptible that in 

 pathological processes a comparison between plastic exu- 

 dations, or blastema, with the matters contained in the 

 ovum, was obviously inadmissible, and that, where really 

 formed parts were found, they had proceeded from a 

 pre-existing part, a cell. 



The mode of origin of new formations is, as it seems, 

 a double one. We have, namely, either to do with a 

 simple division, such as we discussed when treating of 

 irritation (p. 346). We then see the whole series of 



FIG. 124. 



Fig. 124. Proliferation of the growing cartilage of the diaphysis of the tibia of 

 a child. Longitudinal section, a. The cartilage-cells on the border of the epiphy- 

 sis, some of them simple, some of them in a state of commencing proliferation. 



b. Groups of cells that have arisen from the repeated division of simple cells. 



c. Groups of cells lying near the calcifying border of the diaphysis, and considera- 

 bly developed through the growth and enlargement of the individual cells ; the 

 intercellular substance growing continuallv more and more scanty, d. Section of a 

 bloodvessel. 150 diameters. 



