GENERAL SKETCH OF THE CELL 



tive known types of nucleus ; but this subject is still sub judice 

 (p. 39). A transition from 'this condition to nuclei of the ordinary 

 type appears to be given in the nuclei of certain flagellates (e.g. Chi- 

 lomonas and Trachelmonas\ where the chromatin-granules are aggre- 

 gated about a nucleolus-like body, but are not enclosed by a membrane. 1 

 In considering the structure of the nucleus, as seen in sections, we 

 must, as in the case of the cytoplasm, bear in mind the possibility, or 



rather probability, that some of 

 the elements described may be 

 coagulation - products ; for the 

 nucleus is in life composed of 

 liquid or semi-liquid substance, 

 and Albrecht ('99) has recently 

 shown that nuclei isolated in the 

 fresh condition will flow together 

 to form a single body. Most of 

 the main features of the nucleus, 

 both in the resting and in the 

 dividing phases, have, however, 

 been seen in life (Fig. 9), and the 

 principal danger of mistaking 

 artifacts for normal structures re- 

 lates to the finer elements, con- 

 sidered beyond. 



In the ordinary forms of nuclei 

 in their resting state the follow- 

 ing structural elements may as a 

 rule be distinguished (Figs. 6, 7, 



Fig. 13. -TWO nuclei from .he crypts of ^ T ne nuclear membrane, a 



Lieberkiihn in the salamander. [HEIDENHAIN.J , ,, , , ,. ,, , . , 



well-defined delicate wall which 



The character of the chromatin-network 



(basichromatin) is accurately shown. The upper glVCS the nucleus a Sharp Contour 

 nucleus contains three plasmosomes or true and 'differentiates it clearly from 

 nucleoli ; the lower, one. A few fine linin-threads , ,. , TI^' 



(oxychromatin) are seen in the upper nucleus tn e Surrounding Cytoplasm, 

 running off from the chromalin-masses. The wall Sometimes Stains but Very 

 clear^spaces are ccupie, by the ground-sub- sHghtly> and can scarce ly be dif- 

 ferentiated from the outlying 



cytoplasm. In other and perhaps more frequent cases, it approaches 

 in staining capacity the chromatin. 



b. The nuclear reticnlnm. This, the most essential part of the 

 nucleus, forms an irregular branching network or reticulum which con- 

 sists of two very different constituents. The first of these, forming the 

 general protoplasmic basis of the nucleus, is a substance known as linin 



1 Calkins, '98, I. 



