536 CELL DIVISION IN EGGS OF CREPIDULA. 



spindle, are found in many other experiments, — indeed this is one of the most 

 common modifications of mitosis. This phenomenon and its significance will be 

 considered further in the final section of this paper, pp. 550-553, 557-559. 



X. Effects of Hypertonic Sea Water. 

 (Plates LV-LIX.) 



NaCl added to sea water: Figs. 159-172, 182-192, 202-207, 209-213, 217, 220- 



223. Exps. 804-816, 821-832, 839-840, 843-844, 861-865, 965-990, 994, 



1187. 

 MgCl 2 added to sea water: Figs. 197-200, 208, 214-216, 218, 219. Exps. 833- 



835, 841, 842, 845, 846, 866-868, 991, 992. 

 KC1 added to sea water: Figs. 173, 193, 194. Exps. 836-838, 847, 847a. 

 Sugar added to sea water: Exp. 869. 

 Herbst's Ca-free sea water: Fig. 201. Exp. 848. 1 



The effects of hypertonic sea water upon cell division have been studied by a 

 large number of investigators, particularly since Loeb's (1900) epoch-making 

 discovery that artificial parthenogenesis could be induced in sea-urchin eggs by 

 this means. Among the more important works in this field must be mentioned 

 those of O. and R. Hertwig (1887), J. Loeb (1892, 1895 2 , et seq.), Morgan (1894, 

 1896, 1899, 1900), Norman (1896), Driesch (1892, 1895), Herbst (1895, 1900), 

 Wilson (1901, 1901 1 ), Lillie (1901, 1905), BataiUon (1901, 1904), Scott (1906), 

 Treadwell (1902), Lefevre (1907), Kostanecki (1904, 1906, 1908), Konopacki 

 (1911), et al. All of the authors named found that hypertonic solutions led to a 

 retardation or cessation of cell division, while almost all observers have agreed 

 that nuclear and centrosomal divisions may go on after division of the plasma 

 has ceased. Morgan finds that the most characteristic effect of hypertonic sea 

 water is the production of astrospheres, which may appear in large numbers and 

 subsequently fuse together into a few very large ones. He concludes that there 

 is a definite substance (cyanoplasm) which forms the astrospheres, and that if 

 cell division is delayed by hypertonic solutions this cyanoplasm may accumulate 

 to form one or two suns or astrospheres. 



Loeb (1906) supposes that hypertonic solutions act first in a physical way on 

 the plasma by osmotically removing water from the egg and thus preventing 

 cell division, without necessarily affecting the chemical processes by which 

 nuclein is synthesized from constituents of the plasma. In such eggs chromatin 

 may grow, chromosomes may form and divide, and astrospheres may develop, 

 while streaming and contractility of the plasma is interrupted and cell division 

 is stopped. With higher concentration of salts the chemical processes may also 

 be brought to a standstill. 



Further references to the literature of this subject will be made in connection 

 with the various effects produced on the eggs of Crepidula by hypertonic solutions, 



1 This is classified under hypertonic solutions because its effect on cell division was similar to that 

 of a hypertonic solution. 



