No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 339 



newt. He thinks "that certain deutogenic substances are 

 formed in the [germinal] vesicle, perhaps through the agency 

 of the nucleoli, and are then sent forth to share in the building 

 up of the cell," i.e., of the yolk particles. " The nucleoli in 

 the young ^g^ appear arranged along the chromatin threads, 

 and possibly originate from the thread substance." Later they 

 lose this connection, grow larger, and assume a peripheral 

 position within the nucleus. There is apparently no division 

 of the nucleoli ; they " attain their maximum size shortly 

 before their centripetal movement." Having arrived at the 

 periphery of the nucleus, the nucleoli commence to stain less 

 deeply, their contours become uneven, and they then wander 

 back to the center of the nucleus, where they disintegrate. 

 He does not agree with O. Schultze ('87) that the nucleolar 

 particles build up the chromosomes. 



Kaiser ('93) found in the ^^^ of Echinorhynchus bipennis one 

 large, spherical, peripherally situated nucleolus. It disappears 

 before the pole spindle is produced. 



Lustig and Galeotti ('93), mentioned by Lardowsky ('94), con- 

 sider that the centrosome does not proceed from the nucleolus. 



Mertens ('93), ovum of Homo: two or three nucleoli are present, 

 consisting of a central clearer and a peripheral darker portion; 

 it is probable that several smaller ones may fuse together to 

 form a larger one ; they are at first in intimate connection with 

 the chromatin filaments, but later lose this connection and gradu- 

 ally cease to stain with safranin. The Balbianian corpuscle 

 is an extruded nucleolus : " c'est alors aussi que nous nous 

 etondrons quelque peu sur I'expulsion des parties chromatiques 

 du noyaux, expulsion qui parait affecter les memes characteres 

 chez les oiseaux et les mammiferes " ; eliminated nucleoli 

 ("grains chromatiques ") as well as attraction spheres have been 

 described as Balbianian corpuscles. Ovum of Pica: in young 

 ovules there is one nucleolus which arises as follows : at one 

 point in the nucleus the reticulum concentrates itself, and 

 here a certain number of the filaments fuse together, thus 

 producing the nucleolus. The chromatin is at first irregularly 

 arranged in the nucleolus, but " finit par etre egalement dense 

 dans toutes les parties de la tache germinative," and subse- 



