322 A. RICHARDS. 



cytoplasm, for the nuclei do not exhibit any such striking quan- 

 titative differences as does the cytoplasm. The cells do not 

 seem to form a syncytium of which the ground substance is a 

 part, as some writers have stated. The evidence seems to me to 

 indicate that the ground substance bears a relation to the paren- 

 chyma cells similar to that borne by the intercellular matter of 

 connective tissue, for example, to the connective-tissue corpuscle. 

 That the parenchyma cells have definite boundaries is brought 

 out clearly in the Lichtgriin preparations. I have seen no evi- 

 dence for thinking the ground substance continuous with the 

 cytoplasm. The nuclei of the cells show uniformity of structure 

 as well as of size ; they have a chromatin reticulum and usually 

 a nucleolus. The parenchymal cell is thus seen to be a definite 

 structure with a typical nucleus and a varying amount of cytoplasm. 

 Fig. 19 is a resting parenchyma cell of characteristic appear- 

 ance. The cytoplasm is drawn out into strands upon the number 



FIG. 19. A typical parenchyma cell in the resting condition. This cell is from a 

 proglottid in which the sex organs are only partially developed. 



and size of which depends the width of the cytoplasmic band 

 about the nucleus. Parenchyma shows regional differentiation 

 in the relative amount of ground substance and cells and in the 

 modification of the cytoplasmic parts of the cells only. In the 

 younger cells the cytoplasmic strands are less numerous and 

 frequently extend only a short distance. In older regions more 

 cytoplasm is drawn out into the strands, leaving but a thin layer 

 about the nucleus. 



Professor Child has assumed through all his work that the 

 absence of mitotic figures in tissues known to be growing rapidly 

 is evidence of the occurrence of division by amitosis. This as- 

 sumption is, of course, based on good a priori reasoning, but I 



