262 BULLETIN OF THE 



Ed. van Beneden ('76«, p. 65, Figs. 20, 21, '76^, pp. 170, 171, PI. XIII. Figs. 

 20, 21, '76''-^, pp. 1188, 1193, PI. I. Fig. 15, PI. II. Figs. 19, 20) has described 

 a nucleoplasmic network found both in the nucleus of the immense axial cell, 

 and in that of the ectodermic cells of Dicyemidse. It may traverse the nucleus 

 in all parts, or may be more or less restricted. It is not found in young nuclei. 

 The nuclear substance is stained rose-color in osmic acid followed by picro- 

 carmine, and the nucleolus and nuclear membrane bright red, but the net- 

 work is not stained. 



Trinchese ('76«, p. 175, Tav. 11. Figs. 9, 29, and 32-38) confirms the exist- 

 ence of a previously announced ('76 and '76^) network in the substance of 

 the cell and nucleus. In the present paper he shows its existence in epi- 

 thelial cells, connective-tissue cells, and the cells of the albumen gland of 

 Caliphylla mediterranea, and in the cornea of the frog. The points in which 

 the filaments of the network meet present nodes or enlargements ; one of these 

 nodes within the nucleus, somewhat larger than the others, is the nucleolus. 



Studies on ganglionic cells of the retina of sheep, calves, etc. lead Schwalbe 

 ('76) to the conclusion that the nucleus is differently organized at different 

 stages of development. The smallest, and therefore youngest, nuclei (calf) are 

 without the trace of nucleoli, and appear to consist of a uniformly distributed 

 granular mass. This appearance is probably due to a netlike structure, but as 

 yet there is no differentiation into contents and nuclear membrane. In larger 

 nuclei 2-4 nucleoli are found within a clear mass, which is surrounded by a so- 

 called nuclear membrane. Some of the nucleoli are intimately blended with 

 the nuclear membrane, — appear as elevations upon its internal face. These 

 become less conspicuous in larger nuclei, which usually contain but a single 

 nucleolus, which is not attached to the membrane. In the sheep, ox, etc., this 

 internal nucleolus exhibits thread-like prolongations which differ in extent and 

 number in different cells. Schwalbe's interpretation of the observations is as 

 follows. 



The substance of which subsequently the nuclear membrane and the nucle- 

 oli consist — " nucleolar substance " — is at first uniformly distributed through 

 the whole nucleus. This it fills, more or less completely according to the 

 abundance of numerous small vacuoles distributed through it and containing 

 another mass, " nuclear sap." In the growth of the nucleus there is an increase 

 in the nuclear sap, without an essential increase of the nucleolar substance. 

 The result is that the latter is sundered into various portions, one of which 

 occupies the surface of the nucleus (nuclear membrane with its nucleolar ele- 

 vations), while the other portions constitute the one or more contained nucleoli. 

 Further increase in size induces a stretching of the membrane, which in turn 

 causes its elevations to disappear. The whole process is a vacuolation. The 

 nuclear sap, though probably a fluid, is by no means water, but contains al- 

 buminoids, salts in solution, and is at least of complicated chemical composi- 

 tion. The nuclear membrane and nucleoli, whether central or mural, consist 

 of the same lustrous homogeneous substance. 



Schwalbe agrees with Auerbach that in the growth of the nucleus an enu- 



