No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 541 



zum Vorschein, und zwar in unregelmassigen, oft betrachtlichen 

 Entfernungen von einander." When the nuclei wander towards 

 one another the nucleoli move about, " indem sie innerhalb 

 des Kernraums allerlei gerade, zickzackformige, bogenformige, 

 Bahnen durchlaufen, mit einer vergleichsweise erheblichen 

 Geschwindigkeit, so dass zuweilen in weniger als einer Minute 

 Strecken von der Lange des Kern-Durchmessers zuriickgelegt 

 warden " ; during these movements the nucleoli remain perfectly 

 spherical. When the copulation nuclei are apposed the nucleoli 

 in them suddenly disappear, and the mode of this disappearance 

 was determined in one case, though it is exceedingly rapid ; " das 

 Kiigelchen wurde allmahlich blasser und etwas grosser und fuhr 

 dann plotzlich auseinander, ein Wolkchen bildend, welches einen 

 Augenblick darauf nicht mehr zu sehen war." The nucleoli 

 reappear in the resting nuclei, and in the successive genera- 

 tions up to the eight-cell stage have the same cycle of changes, 

 except that in each generation they are somewhat larger than 

 in the preceding. These nucleoli are formed independently of 

 one another. By the re-formation of the nuclear vacuole a 

 number of cytoplasmic granules pass into the cavity of the 

 nucleus, and there fuse to form the nucleoli. 



Reinhard ('82, cited by Braem, '97) describes in the &gg of 

 Pliimatella different stages of the nucleoli, which may be single, 

 double, or even trilobular. 



WiSTAR Institute of Anatomy and Biology, 

 Philadelphia, February 3, 1897. 



