No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 279 



pas que les differences constatees dans la forme de la tache 

 germinative ne doivent etre attribues a la contractilite de la 

 substance des nucleoles." The vacuoles in the nucleoli are 

 probably "le resultat de I'union momentanee de certaines 

 parties de la substance nucleolaire avec le sue nucleaire." 

 Before its disappearance the nucleolus breaks into fragments, 

 which then dissolve in the "substance nucleaire." In this 

 fragmentation one fragment is always larger than the others, 

 and contains the vacuole of the primitive nucleolus; it persists 

 until all the smaller fragments have disappeared. 



Biitschli ('76) found that the nucleolus disappears before the 

 formation of the first pole spindle in TylencJms, Anguillula, 

 Notommata, Brachiomis, Triarthra, Aphis. He mentions that 

 von Siebold, in 1848, first introduced the name " nucleolus " for 

 the micronucleus of the Infusoria, and compared it with the 

 nucleoli of metazoan cells. He also cites some of the earlier 

 writers who compared the pole bodies with nucleoli. 



O. Hertwig ('76) calls the nucleolus "das wichtigste Form- 

 element des Kerns," and terms its substance " Kernsubstanz " 

 in opposition to the " Kernsaft " (compare his brother's paper 

 of the same year). In the process of maturation he holds that 

 " der Eikern der aus dem Keimblaschen frei gewordene oder 

 ausgewanderte Keimfleck ist." He noticed vacuoles in, but not 

 amoeboid movements of, the germinal spot of Toxopneustes 

 lividus; he observed such motions, however, in the germinal 

 spots of Ratia and PterotracJiea. 



R. Hertwig ('76) terms the dense substance of the nucleolus 

 " Kernsubstanz." " Entweder leiten sich die vielen Kern- 

 korper direkt aus dem homogenen Zustand des Kernes ab, 

 indem die Aussonderung der Kernsubstanz an verschiedenen 

 Punkten gleichzeitig begonnen hat ; oder die zahlreichen 

 Nucleoli sind, . . . durch Theilung aus einem ursprunglich 

 einfachen Nucleolus entstanden." He believes that the 

 " Nucleoli die Trager der Kernfunction sind. . . . Somit 

 miissen wir in alien den Fallen, in denen sich ein oder mehrere 

 Nucleoli im Kerne differenziren, in diesen die Thatigkeitscen- 

 tren des Kernes erblicken." 



Schwalbe ('76) studied the nuclei of retinal ganglion cells of 



