5oS MONTGOMERY. [Vol. XV 



matin, and considers the nucleoli to be only isolated masses of 

 chromatin surrounded by linin sheaths ; these observations 

 have not been corroborated by any other wrriters and would seem 

 to be due to faulty methods of fixation. 



In opposition to Meunier ('86), and in agreement with most 

 investigators, I must conclude that vacuoles are normal struc- 

 tures in nucleoli, since they may be seen after the most diverse 

 methods of fixation, and their size and number are not only to 

 some extent limited for the particular cell, but are also different 

 at different periods in the metamorphoses of the nucleus. It is 

 the rule that the youngest nucleoli are homogeneous, and that 

 vacuoles first arise when they have increased in size. Their 

 size and number vary at different phases in the development 

 of the nucleolus. Very frequently a number of smaller ones 

 appear, and then these subsequently fuse together and produce 

 a larger one. The nucleoli of egg cells are characterized as a 

 rule by more numerous or larger vacuoles than those of somatic 

 cells, and in many somatic cells these vacuoles appear to be 

 wholly absent. The vacuolar substance appears in some cases 

 not to be a derivative of the ground substance of the nucleolus, 

 but to be derived from without the nucleolus (ova of Doto and 

 MoHtagica). Perhaps this vacuolar substance always has an 

 extranuclear origin, since in many cases a germinal spot grows 

 larger merely by an increase in its volume, while the ground 

 substance seems neither to increase nor diminish. 



The alveolar structure of nuclei as described by Purcell ('94), 

 Schaudinn ('94), Korschelt ('95), and Lauterborn ('95b) is prob- 

 ably referable to the regular distribution of equal-sized vacuoles 

 in the nucleolus. 



A " Kernkorperchenkreis," a shell of minute granules 

 arranged concentrically around the nucleolus, has been de- 

 scribed by Eimer ('71, '72), Auerbach ('74a, who considered it 

 to be the result of opposing repulsive forces of the nucleolus 

 and nuclear membrane). Brass ('89), Pflucke ('95), Platner ('89a), 

 Smirnow ('90), Engelmann ('80), Carnoy and Lebrun ('97a). A 

 more or less similar phenomenon has been described by me for 

 ganglion cells of Doto. Such a nucleolar circlet must be con- 

 sidered, in most cases at least, an artefact. But in this cate- 



