GENERAL ANATOMY. 



79 



substances. Formerly, on this account, it was in very many 

 cases overlooked, and, even yet, it can often be demon- 

 strated only by the exercise of great care, and by employ- 

 ment of a special technique based upon the peculiar reac- 

 tion of the nuclear substance. 



The Nuclear Substance. The nuclear substance is 

 distinguished from protoplasm among other ways by its 

 greater coagulability in certain acids, e.g., acetic and 

 chromic acids, which therefore are often used for demon- 



FrG. 10 Vesicular nuclei with different arrangements of the nuclear substance, a, Egg 

 nucleus of Toxapneustes lividus ; d, germinal vesicle of the same animal ; /;, c, nuclei 

 of Actinosphcerium Eichhorni ; e, nucleus of an Acantliometra ; _/", ^, nuclei of the 

 salivary glands of Culex pipiens (larva). 



strating the nucleus. If in a living cell the nucleus is 

 invisible on account of the similarity of its refraction to 

 that of the protoplasm, the addition of 2% acetic acid will 

 often bring it into sharp contour. 



Structure of the Nucleus. The distribution of the 

 nuclear substance in the nucleus is very varied (Fig. 19); 

 often it forms ? spongy network of larger or smaller meshes 

 running throughout the whole cell (a, g), or it is collected 

 into a single large or several small bodies, the nucleoli 

 (mono- and pluri-nucleolated nuclei) (7>, r), or the forma- 

 tion of nucleoli is combined with a nuclear network (V, /) ; 

 a part of the nuclear substance lying in the periphery may 

 even produce a continuous superficial crust (< ). By this 

 arrangement there is left a more or less considerable space 

 between the meshes of the nuclear network or between the 



