l6o BIOLOGICAL LECTURES. 



nucleus suddenly commences to contract, and by the withdrawal 

 of its pseudopodia gradually to assume the spherical form again. 

 Now the point of chief interest to us is, that during the process 

 of nuclear contraction the nucleoli are discharged into the 

 cytoplasm. And the appearance of concentric rows of dis- 

 charged nucleoli within the cytoplasm leads to the conclusion 

 that the nuclear contraction is not gradual, but sudden and 

 intermittent. The case is as if one holds in his hand a sponge 

 filled with water, and by successive pressures of the hand forces 

 out the water in jets ; so by the contraction of the nucleus, 

 which is automatic, as shown by the retraction of its pseudo- 

 podia, the nucleoli are forced out through the nuclear mem- 

 brane into the cytoplasm, where the pressure is less. And the 

 nucleolar substance in the cytoplasm is found in the form of 

 rods, radial to the surface of the nucleus, which proves that it is 

 forced out rapidly in streams. But a remarkable point remains 

 to be noted : one nucleolus, and one only, appears in every case 

 to be retained within the nucleus ; for this phenomenon I can 

 give no explanation, since this one does not appear to differ 

 chemically from the others. Finally the nucleus becomes as 

 small as it was at the commencement of the prophase and 

 gradually rounds off ; no longer are secretion globules present 

 in the cytoplasm ; and the extranuclear substance gradually 

 disappears, — Jioiv, it is impossible to determine, though since 

 it is not discharged through the cell duct, and there is no evi- 

 dence of any migration through the cell membrane, it would 

 seem probable that it becomes dissolved within the cytoplasm. 

 Such is the history of a cycle of functional activity. 



In these remarkable stages certain salient points are to be 

 noted : the increase, first in size and then in number, of the 

 nucleoli, accompanying the formation of the secretion ; and the 

 discharge of nucleolar substance following upon the extrusion 

 of the secretion. These phenomena would point to some con- 

 nection between formation of nucleolar and secretory substances, 

 which is rendered the more probable, since by its extreme 

 amoeboid form the nucleus appears to be in close physiological 

 connection with the cytoplasmic processes. The fact that the 

 secretion globules appear first in the cytoplasm at some distance 



