218 Cakolink McGir.L, 



The cells in the gi'owth area are characterized by the greatest 

 activity of all parts, especially of the nucleoli and yolk-nuclei; in 

 fact, rapid metabolic chang^es are everywhere taking' place throuah- 

 out the cell. 



(a) The Nucleoli. 



At the beg-inning- of the growth period, the nucleolus consists^ 

 of a doubly staining- body made up of basiphile and oxyphile sub- 

 stances arranged either as in Fig. 8. side by side, or, as in several 

 cells in Fig. 9, with the basiphile forming a layer around the oxy- 

 phile substance. At this time most of the chromatin of the cells 

 is in the nucleolus. Soon the oxyphile nucleolus begins to multiply 

 (Fig. 13), and these bodies pass out of the basiphile mass into the 

 nucleus (Fig. 10 — 38). Sometimes ihe condition shown in Fig. 11 

 is seen, where several oxyphile bodies are present at the same 

 time in the basiphile nucleolus; most frequently they pass out into 

 the nuclear sap as soon as thej' are well formed, so that the usual 

 arrangement is like Fig. 16, 17. 26, etc., where the completely formed 

 nucleolus is at the periphery, passing out of the basiphile mass, and 

 a vacuole of greater or less size is left inside. Often before the 

 oxyphile nucleolus has passed entirely out. a new oxj^phile bodj- 

 has begun to form in the centre of the vacuole (Fig. 10 and 23 1. 



During this stage of high metabolic activity, the basiphile bod}' 

 becomes much vacuolated, so that with iron-haematoxylin. it stains 

 lighter than the denser, more homogeneous oxyphile nucleolus. Sa 

 many vacuoles may be present that they give the structure a honey- 

 combed appearance (Fig. 17. 20. 26. 35. 36, etc.). Often in the 

 larger vacuoles a chromatin reticulum is seen (Fig. 22, 27 and 38). 



There is very good evidence that the oxyphile bodies ai-e formed 

 from the basiphile substance, for, aside fi'om the fact that all sizes 

 of them are seen on the inside of the latter, there is often a mixing' 

 and blending of the diiferential stains, as in Fig. 35 and 36, indi- 

 cating that chemical changes are going on whereby nuclein may be 

 converted into para-nuclein. This establishes pretty clearly the 

 close relationship between the two substances. 



As the oxyphile bodies pass out into the nucleus, they dissolve 

 in the nuclear sap. This solution takes place slowly, so that at 

 times several of the bodies may be seen in a single nucleus (Fig. 14, 

 22 and 25). That they are dissolved in the nuclear sap is proved 

 by the following facts: first, as they move away from the basiphile 



