52 THE GERM-PLASM 



cal or occasional migration of these biophors into the cell-body, 



where they multiply, and become arranged in obedience to the 



forces acting within them. The difficulty of ascertaining the 



actual mode of arrangement is nowhere greater than in the case 



J of the higher unicellular forms. How is it possible that the 



j nucleus should always allow only those kinds of biophors to 



migrate which are required to replace those structures lost by 



r^division ? And why do these biophors always move either in the 



1 direction of the missing oral region, or towards tFe posterior end 



^ of the body, according to which parfsTi-e wanting in tlie^wo 



daughter-animals? For the present these questions are un- 

 answerable ; and in the meantime we must be content with 

 having shown how the materials for the construction of the 

 cell-substance are transmitted from mother to daughter, and in 

 what way they are placed at the disposal of the forces acting in 

 the. cell-body. 

 ^^ The experiments made by Nussbaum * and Gruberf on the 

 artificial division of Infusoria prove that the nucleus really 

 controls the cell-body. These observers found that only those 

 j pT)rtions which contained a part of the nucleus were capable of 

 giving rise to a complete animal ; the other pieces lived for a 

 j time, and then perished. One of Gruber's observations also 

 tends to show that when regeneration of missing parts occurs, 

 the nucleus sends out invisible material particles into the cell- 

 body. He cut a large Stentor which was preparing for division 

 , transversely into two parts, so that the posterior portion con- 

 jtained no trace of the nucleus, and then obser\-ed that regenera- 

 tion of the missing parts nevertheless took place, especially in 

 the oral region. If the control of the cell depended on the 

 emitted influence of the nucleus, this regeneration would be 

 totally inexplicable; if, however,_biQpliors proceed from ^ the 

 nucleus into the cell-body when regeneration is to take place, 

 this might have already occurred in an animal preparing for 

 division, as this one was before it was artificially divided. 



The descendants of unicellular animals are similar to their 

 ancestors : two daughter-cells are produced by the division of 



* Nussbaum, ' Ueber die Theilbarkeit der lebenden Materie,' Archiv. f. 

 mikr. Anat., 1886. 



t Gruber, ' Ueber kiinstliche Teilung bei Infusorien," ' Biol. Centralblatt,' 

 Bd. iv. ; and ' Beitrage zur Kentniss der Physiologie und Biologic der Pro- 

 tozoen,' Ber. d. naturf. Gesellsch. zu Freiburg i/Br., 1886. 



