HI. 8 CHEMICAL COMPOSITION 127 



The effects of nicotine are perhaps the most striking (Fig. 68, a-e). 

 Various solutions 1 % and less of a concentrated extract were 

 allowed to act upon the egg for different lengths of time (five to 

 fifty minutes) before fertilization ; the ova were then replaced in 

 sea- water and fertilized. The cytoplasm is so paralysed by the 



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3 : : : #: 







FIG. 68. The effect of alkaloids and other poisons on the processes 

 of fertilization and nuclear division in the egg of the sea-urchin, 

 Strong ylocentrotiis lividus. (After R. and 0. Hertwig, 1887.) 



a. The egg was exposed to nicotine (one drop in 200 c.c. of sea- water) 

 for ten minutes, and then fertilized ; drawn fifteen minutes later. 



ft, c. The same for fifteen minutes ; drawn after one and a half hours. 



d. The same for ten minutes ; drawn after three hours, ten minutes. 



e. The same ; drawn after three hours. Only part of the complex 

 figure is shown ; the remainder lies in another plane. 



/, g, h. Exposed to a 0-05% solution of quinine for twenty minutes one 

 and a half hours after fertilization ; drawn from one to two hours later. 

 k. 1-5, male pronucleus, 6, female pronucleus. Exposed to chloral 

 (0-5%) one minute after fertilization ; fixed after 150 minutes. 



I, m. Chloral 0-5% one minute after fertilization ; fixed after six hours. 

 Male and female pronuclei reconstructed and metamorphosing, in m 

 the ' fan ' form with commencing division. 



n, o. Placed in chloral 0-5% five minutes after fertilization ; preserved 

 after ninety minutes. 



n. Female pronucleus (four-rayed rosette), and male pronucleus 



(three-rayed rosette). 

 o. Fusion of pronuclei. 

 p. The same. Female pronucleus in the pseudo-tetraster forms. 



