184 AGE, GROWTH, AND DEATH 



the size of nuclei is by no means a simple one. It 

 has been found, for instance, in the experiments made 

 upon some of the simple algse, the so-called Spirogyra, 

 which every elementary student of botany probably 

 has looked at in the laboratory, that by certain arti- 

 ficial conditions, as made in the experiments of Pro- 

 fessor Gerassimow, 1 the size of the nucleus can be 

 changed in the cells, and when the size of the nucleus 

 is changed, the size of the cell alters also. Professor 

 Richard Hertwig has made some very interesting 

 experiments, 2 proving that in the case of certain pro- 

 tozoa, the size of the nucleus varies with the tempera- 

 ture ; he says of Dilepta, the form experimented on, 

 " Kiihle Temperatur veranlasst grosse, warme Tem- 

 peratur kleine Kerne" (p. 10). We considered a few 

 moments ago the reduction in the size of nuclei dur- 

 ing the early stages of the embryonic development. 

 Later, however, there is again an increase of size in 

 the nuclei, occurring during the later embryonic 

 development and during youth. Recently K. A. 

 Heiberg 3 has given some data, from which I have 



1 J. J. Gerassimow, " Ueber den Einfluss des Kerns auf das Wachsthum der 

 Zelle," Bulletin Soc. Itnper. Naturalistes, Moscou, 1900, pp. 185-220. 



" Die Abhangigkeit der Grosse der Zelle von der Menge ihrer Kernmasse," 

 Zeltschrift f. allgem. Physiologic, i., 220-258. 



" Uber die Grosse des Zellkernes," Beihefte z. Botan. Centralblatt, xviii., 

 45-118. 



" Zur Physiologic der Zelle," Bulletin Soc.Impdr. Naturalistes , Moscou, 

 1904, pp. I-I34- 



' 2 Richard Hertwig, " Ueber das Wechselverhaltniss von Kern und Proto- 

 plasma " (see pages 10 ff.), Sitzungsber. Gesell. Morphol., Miinchen, 1902-3. 



3 K. A. Heiberg, " Ueber eine erhohte Grosse der Zelle und deren Theilebei 

 dem ausgewachsenen Organismus, verglichen mit dera nicht ausgewachsenen," 



