532 MONTGOMERY. [Vol. XV. 



though the mode of disappearance of this substance may be 

 more or less dependent upon the mode of mitosis, the substance 

 of the parent-nucleolus may be in many cases not transferred 

 to the daughter-nuclei, but the latter (perhaps as a rule) may 

 produce their own nucleoli dc novo. 



Strasburger ('93, '97) assumes that the small granules found 

 by Kostanecki ('92) in the equatorial plate of the central spindle 

 may be nucleolar particles, and accordingly that the nucleolar 

 substance may be in this way very evenly distributed to the 

 daughter-nuclei ; but it is not as yet clearly shown that these 

 granules are derivatives of the nucleolus (cf. also Debski, '97, 

 Sala, '95, Pfitzner, '86b, and Rosen, '95). 



Zacharias ('85), Carnoy ('85), and Plainer ('86) have concluded 

 that in some cases the achromatic spindle fibers are derived 

 from the nucleolus ; similar views are held by Strasburger ('95, 

 '97), Harper ('97), and Fairchild ('97), but most facts would show 

 this view untenable. 



Rhumbler ('93) assumes that a greater amount of nucleolar 

 substance is accumulated in the nucleus before mitosis than is 

 necessary for its growth, and this superfluous amount would 

 serve for the formation of the nucleoli in the daughter-nuclei. 



12. Tlic Function of the Nucleolus. 



The attempt to deduce the physiological economy of a struc- 

 ture from a mere study of its morphological relations is always 

 difficult, and this is especially the case with regard to the 

 nucleoli. 



Balbiani ('64) found contractile and discharging vacuoles in 

 the germinal spot of Plialangium, and notes that they differ 

 from the contractile vacuoles of the Rhizopoda in that they 

 are not formed again at the same point. Hacker ('93c) regarded 

 the nucleolus of the ovum of Eckmus as an excretory organ, 

 since he found its large vacuole to be contractile ; he compared 

 it directly to the contractile vacuole of Infusoria. Balbianj 

 ('65b) also observed contractile vacuoles in the germinal spots 

 of Helix, Vortex, and Prostonium, and in these the vacuole dis- 

 charges through a small orifice in the cortical substance of the 



