ITS CHEM1CO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 49 



Moreover, the nuclein is not always spread out upon a frame- 

 work. For example, the large vesicular nuclei of Chironomus larvce 

 (Fig. 27) enclose, as Balbiani (II. 2) has discovered, a single thick 

 nuclear thread ; this is variously twisted, and in stained prepara- 

 tion is seen to be composed of regular alternately stained and 

 unstained layers. This has also been observed by Strasburger in 

 some plants. The two ends of the thread terminate in nucleoli. 



Further, in other cases the greater part of the nuclein is collected 

 into a large round body, which looks like a nucleolus, but which is 

 really very different from the above-described true nucleoli, which 

 contain paranuclein (p. 42). In order to avoid confusion it is best 

 to call such bodies nuclein corpuscles. As an example of this class 

 the nucleus of Spirogyra may be mentioned ; the nuclei of many of 

 the lower organisms are very similar to it in structure. It consists 



FIG. 26. FIG. 27. 



FIG. 26. Nucleus, about to divide, of a cell from Afcarix megalocephala bivalens, with the 

 eight nuclear segments arranged in two bundles, and with two pole corpuscles (Hertwig 

 II. 19 b, Tab. II., Fig. 18.) 



Fi. 27. Structure of the nucleus of a cell from the salivary gland of Chironomus. (After 

 Balbiani, Zoolog. Anzeiger, 1881, Fig. 2.) 



of a vesicle which is separated from the protoplasm by a delicate 

 membrane, and which contains a fine nuclear framework. Since 

 this is incapable of retaining the dyes of staining solutions, it is 

 evident that it consists chiefly of linin, upon which only a few 

 nuclein granules are deposited. One large nuclein body is present 

 in the framework ; occasionally, however, it is divided into two 

 smaller ones. That this body really consists of nuclein is proved 

 partly by its behaviour towards staining solutions, but chiefly by 

 the fact that during nuclear division its substance breaks up into 

 granules, thus forming the nuclear segments. 



Similar nuclein bodies, which in literature generally go under 

 the name of nucleoli, play a very important part in the structure of 

 the germinal vesicles of animal egg-cells. These germinal vesicles 



