32 HEREDITARY CHARACTERS 



(Sphxrechinus granularis) with a sperm of another species 

 (Echinus microtuberculatus). Some of these fertilised frag- 

 ments developed into dwarf larvae, and these larvae exhibited 

 nothing but the paternal characters. 1 



There is also a good deal of evidence suggesting that the 

 nucleus controls all the functions performed by a cell, and this 

 is interpreted by some as meaning that-, the lines along which 

 the cells will develop depend upon the nucleus or upon 

 something contained within it. It has been shown in the 

 case of many unicellular animals, that if they be divided 

 into small pieces, those which contain even a minute portion 

 of the nucleus will regenerate into a perfect animal with all 

 its parts and organs. The rate at which this regeneration 

 takes place depends upon the size of the portion of nucleus 

 contained. On the other hand, fragments of cytoplasm 

 which are devoid of any portion of nucleus die in a com- 

 paratively short time. For a certain period they are able 

 to move about, and even to engulf food particles, but they 

 are unable to digest, and regeneration never takes place. 2 

 There is evidence also of the supreme importance of the 

 nucleus in the case of the cells forming the bodies of multi- 

 cellular animals. As an instance of this we may take what 

 happens when a nerve fibre in an animal is divided. The 

 peripheral portion, that is, the part which is separated from 

 the nucleus, proceeds to degenerate ; the proximal portion, 

 that is, the part which is still connected with the nucleus, 

 sends out a new fibre which takes the place of the degene- 

 rated portion. 



In addition to these observations, we must remember 

 that it has been clearly demonstrated in many organisms 

 that not only do half the chromosomes appearing in the 

 first division of the fertilised ovum come from the male and 

 half from the female parent, but that these groups of chromo- 



1 Boveri, Th., " Uber die Befruchtungs- und Entwickelungsfahigkeit kern- 

 loser Seeigel-Eier," Archivfiir Entwidclungsmechanik, ii. 3, 1895. 



2 Gruber, A , " Mikroskopische Vivisektion, " Berichte der Naturforschender 

 Gesellschaft, Freiburg, vii., 1893. 



