520 MONTGOMERY. [Vol. XV. 



wholly out of place in the present paper on the true nucleolus, 

 since they are necessary to prove that the true nucleolus is in 

 all cases never derived from the chromatin ; where " nucleoli " 

 have been described as arising from the chromatin elements of 

 the nucleus, such structures cannot correctly be included under 

 the term " nucleolus," when the latter is used in the proper 

 sense. 



8. Relation between Nucleoli and Centrosomes. 



The greater number of cytologists agree that there is no 

 genetic relations between these two structures ; and my obser- 

 vations on the egg of Piscicola as well as more recent studies on 

 other objects corroborate this view. But some few have been 

 led to contrary conclusions by observing the fact that in mitosis 

 the nucleolus often disappears about the time that the centro- 

 some becomes apparent. Thus Karsten ('93) assumes that the 

 nucleoli wander out of the nucleus into the cytoplasm, and 

 there become the centrosomes of the spindle ; this observation 

 has been refuted by Humphrey ('94). Also Wasielevsky ('93) 

 believes that the centrosomes of the egg of Ascaris stand in 

 some connection to the nucleoli, but this stands in direct oppo- 

 sition to the conclusions of all other workers on this object, 

 except those of Carnoy and Lebrun ('97b), and the supposition 

 of Sala ('95). Then Lavdowsky ('94) concludes that the nucleo- 

 linus is the centrosome in the process of formation, but he failed 

 to observe the steps by which this body develops into a centro- 

 some. Further, Julin ('93b) is said by Delage ('95) to have 

 assumed a genetic relation between the centrosome and the 

 nucleolus. Other supporters of the nucleolar origin of the cen- 

 trosome : Balbiani ('95), Wilcox ('95), Bremer ('95b), F. Toyama 

 ('94). I believe that these are the only investigators who have 

 assumed this genetic relation. We may conclude, from the 

 greater number of observations at hand, that there is probably 

 no connection between these structures in the metazoan cell. 

 But it is difficult to decide the homologies of the body found by 

 Keuten ('95) in the nucleus of Ccratimn, and termed by him 

 nucleolo-centrosoma ; he considers it as equivalent to the central 



