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 

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

 nucleus should always allow only those kinds of biophors to 

 migrate which are required to replace those structures lost by 

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

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

 of the body, according to which parts are wanting in the two 

 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 Gruber f on the 

 artificial division of Infusoria prove that the nucleus really 

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

 portions which contained a part of the nucleus were capable of 

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

 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 Steiitor which was preparing for division 

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

 tained no trace of the nucleus, and then observed 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, biophors 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 Physiologic und Biologic der Pro- 

 to^oen,' Ber. d. naturf. Gesellsch, zu Freiburg i/Br., 1886. 



