Xncleoli during- the Oogenesis of the Drag-on-fly. 209 



GuiGNARD (1885) and Hertens (1893). These observers think that 

 it arises simply as a concentration of the chromatin reticulum. 

 Another idea is that the nucleolus is derived indirect!}^ from the 

 chromatin by chemical transformation, whereby nuclein, the chemical 

 constituent, is changed into para-nuclein. In its reaction to stains 

 it passes from basiphile to oxyphile. Schneider (1891) holds this 

 view and Obst (1899i worked it out in greater detail. The latter 

 tinds in resting nuclei that the basiphile chromatin-granules undergo 

 chemical changes, becoming oxj-phile, the oxyphile granules then 

 fusing to form the nucleoli. 



2. Double Nucleoli. 



In a single nucleolus there are frequently present nucleoli of 

 both oxyphile and basiphile staining substances. Often the two 

 kinds of nucleoli unite to form single structures, which, because of 

 their double staining qualities are known as double nucleoli. The 

 usual arrangement in such nucleoli is a central mass of oxyphile 

 substance, with the basiphile substance forming a layer around it. 



Only a few of the many writers who have noted the occurrence 

 of double nucleoli can be mentioned in this brief review. 0. Hertwig 

 il876, 1877, 1878) describes nucleoli of two substances in Medusae, 

 Siphonophora, Gastropoda, Lamellibranchia, Asteroidea, Echinoidea 

 and Ascidiae. In most cases the two substances lie bound together, 

 side by side. However, in Ascidia and Siphonophora, the para- 

 nuclein forms the central granule of the nucleolus and has the 

 nuclein wrapped around it. Hermann (1899) finds double nucleoli 

 in the spermatoblasts of the mouse. Lönnberg (1892) in Doris 

 proxima and Mijtilus, observed similar nucleoli. Stauffacher i 1893) 

 in Cyclas cornea. Montgomery (1899) in Montctfjua, Polydora and 

 Piodalia, find double nucleoli. Obst (1899) in Mollusca and Arachnida 

 describes two kinds of nucleoli which are separate in early stages, 

 but fuse to form double nucleoli in later development. Guenther 

 11903) in resting Echinoderm eggs finds double nucleoli, each having 

 a central granule of oxyphile substance with all the chromatin of 

 the egg wrapped as a layer of basiphile substance around it. Hatai 

 (1904) in the spinal ganglion cells of the white rat describes nucleoli 

 of two staining substances. He, moreover, gives good evidence that 

 the one substance may be derived from the other, for his material 

 shows all stages in transition from basiphile to oxyphile staining 

 qualities, and vice-versa. 



