256 BULLETIN OF THE 



nucleoli (1-3) increase gradually in number as the vesicle grows older, and 

 often lie in close proximity to the membrane. 



Similar observations are made (pp. 425, 432) on the nuclei of mammalian ova. 

 " The nucleus of the cells [germinal epithelium] loses its more or less distinct 

 network, and becomes very granular, with a few specially large granules (nu- 

 cleoli). The protoplasm around it becomes clear and abundant, — primitive 

 ovum stage." " A segregation takes place in the contents of the nucleus within 

 the membrane, and the granular contents pass to one side, where they form an 

 irregular mass, while the remaining space within the membrane is perfectly 

 clear. The granular mass gradually develops itself into a beautiful reticulum, 

 with two or three highly refracting nucleoli, one of which eventually becomes 

 the largest and forms the germinal STpot par excellence." Klein's statement that 

 the " nucleoli " are accumulations of fibres is too sweeping, according to Balfour, 

 since nucleoli often exist in the absence of a network, and the latter is certainly 

 wanting in primitive ova. The differences of opinion between Balfour and 

 Klein, are not very radical, however, for the former considers that both network 

 and nucleoli are composed of the same material, : — nuclear substance. 



There are probably no tissues in which the structure of the nucleus has been 

 more attentively studied than in the ganglionic cells of nerve centres. It is 

 the magnitude often attained by them, as well as the lively controversy concern- 

 ing the relation of the nerve fibres to them and their nuclei, which has tended 

 to make the latter the objects of oft-repeated observations. 



In 1846 the studies of Harless ('46, p. 287) on the ganglionic cells of the 

 lobi optici in the torpedo pointed to the union of the nucleolus with one or 

 two nerve fibres. After treatment with iodine the fibre (Nervenprimitivfaser) 

 may be traced, says Harless, as a light yellow streak, through the more deeply 

 colored ganglionic body, up to the nucleus of the inner cell [i. e. up to the 

 nucleolus]. 



Similar conclusions were reached by Axmann ('47) and Lieberkiihn ('49), 

 whose results are cited by Stilling ('56-'59, pp. 807, 814, 821).* The last 

 author, though unable to confirm these observations, maintains ('56-59, pp. 783- 

 787, 793-796, Taf. XXV.) that the parenchyma of cell, nucleus, and even nucle- 

 olus is traversed, without recognizable order, by numerous extremely fine tubes 

 (Elementarrohrchen), which together form a dense network. Open as these 

 studies of Stilling doubtless are to the severe criticisms which have been urged 

 against them, they nevertheless may not be exclusively the result of a failure to 

 distinguish between artificial and natural appearances. Recent studies make 

 very probable the existence of a greater complication of nuclear structure than 

 has hitherto been generally accepted, though not lending any direct support to 

 Stilling's views of the tubular nature of the filaments he has depicted. 



Wagener ('57) defends Lieberkiihn from the criticisms of Stilling ('56), and 

 adds evidence drawn from the study of nerve-cells in Hirudo, Limax, etc., to 

 show the existence of the nucleolar fibre. 



* See also Stilling, '56. 



