136 GROWTH 



a variable degree in all organs. Especially the relative amount 

 of stroma varies according to age. 



Table II 



VOLUMETRIC CHANGES IN THE CONSTITUENT TISSUES AND 



CELLS OF THE HYPOPHYSIS AND SUPRARENAL GLANDS 



IN THE ALBINO RAT, NEWBORN AND ADULT 



Jackson 24 ' 25 



Hypophysis (pars anterior) Newborn Adult 



Per cent Per cent 



Parenchyma 93-3 8 9-4 



Stroma and blood vessels 6.7 10.6 



Cytoplasm of parenchyma cells 66.0 80.0 



Nuclei of parenchyma cells 3+.0 20.0 



Suprarenal Cortex (average) 



Parenchyma 87.7 86.6 



Stroma and blood vessels 12.3 x 3-4 



Cytoplasm of parenchyma cells 66.6 82.4. 



Nuclei of parenchyma cells 33-+ x 7-6 



Suprarenal Medulla 



Parenchyma 67.2 72.3 



Stroma and blood vessels 32.8 27.7 



Cytoplasm of parenchyma cells 54.0 90.4 



Nuclei of parenchyma cells 46.0 9.6 



VI. Cell Changes in Development 



The analysis of the growth process thus leads us back to our 

 starting point, the cell. Morphogenesis, like other vital phe- 

 nomena, becomes ultimately a cell problem. While time permits 

 only a brief consideration of the cell changes during develop- 

 ment, a few of the more important aspects may be mentioned. 

 These include the related cell changes in (i) number, (2) 

 form, (3) position, (4) size, and (5) structure. 



1. Cell number. With reference to cell division, Bizzozero 4 

 classified the cells of the body under three types — permanent, 



