66 INTRODUCTION TO CYTOLOGY 



of the cell (Haecker). Strasburger (1895, 1897), who observed the dis- 

 appearance of the nucleolus at about the time the spindle fibers appear 

 during the prophases of mitosis, concluded that it is a mass of reserve 

 kinoplasm which gives rise indirectly to the achromatic figure. While 

 some have agreed in the main with this conclusion, many have denied 

 the relationship of nucleolus and spindle, contending that the former is 

 rather a reserve constituent for the linin reticulum (Eisen 1900) or the 

 chromatin (Schurhoff 1918). Frequently the bulk of the basichrom- 

 atic material of the nucleus is lodged in the nucleolus at certain stages. 

 In the somatic nuclei of Marsilia (Fig. 17, E), for example, Berghs (1909) 

 shows that it is transferred to the nucleolus during the telophases of 

 mitosis, and returned to the reticulum in the following prophases. This 

 phenomenon, which has an important bearing on the role of the chrom- 

 atin and the individuality of the chromosomes, will be referred to again 

 in Chapter VIII. 



In many cells, as shown by the work of the zoologists the nucleolus 

 appears to be concerned in the elaboration of secretion and storage prod- 

 utts. In the eggs of certain animals Macallum (1890) showed that 

 the nucleolar material, which appears to differentiate from the chrom- 

 atin, passes into the cytoplasm and there combines with another 

 substance to form the yolk globules. In the cells of the pancreas he 

 further found that material often present in the form of nucleoli func- 

 tions in a similar manner in the production of zymogen. Many other 

 observations of this general nature have been reported. In the silk- 

 gland cells of certain insects it has recently been shown by Nakahara 

 (1917) that some of the nucleoli, which may originally be passive by- 

 products, later pass into the cytoplasm and contribute to the formation 

 of the secretion products. An extreme view of the importance of the 

 nucleolus is that of Derschau (1914), who regards the nucleolus as the 

 real center of the life of the cell. Granules of oxychromatin, he asserts, 

 pass out from the nucleolus through the cytoplasm in the form of chon- 

 driosomes, carrying basichromatin as a building material to the places 

 where it is required. 



It is highly probable that the nucleolus has various functions in dif- 

 ferent cells, but in general we maj r conclude that it is a mass of accumu- 

 lated material which is usually, though not always, utilized in the 

 metabolic processes of the nucleus 



The Nuclei of Bacteria and Other Protista. — The question of the 

 nucleus in bacteria is one that it appears to be particularly difficult 

 to settle satisfactorily. This is due not only to the minute size of these 

 'organisms, which makes special methods necessary and observation very 

 difficult, but also to the fact that a variety of conditions seems to be 

 present in the group. That the bacterial cell is devoid of a nucleus has 

 been held by several investigators including Fischer (1894, 1897, 1899, 



