PHASES OF DIVIDING SEA-URCHIN EGG. 127 



washed with a stream of water from the medicine-dropper, and 

 set aside to undergo development. The proportion proceeding 

 with development to the free-swimming larval stage was sub- 

 sequently determined. It was found that the estimate of the 

 proportion surviving to the blastula stage was more readily and 

 exactly made, if the watch glass containing the eggs was removed 

 from the bowl of sea-water just before the free-swimming larval 

 stage was reached. Thus all survivors could be confined within a 

 small volume, and the count or estimate easily made. As a rule, 

 the experiments were carried only up to about the time of second 

 cleavage; since the evidence indicates that the same variation of 

 susceptibility occurs in each cell division cycle; moreover diver- 

 gencies between the different eggs in any lot become more pro- 

 nounced as time elapses, and it is important that all eggs of a lot 

 should be in the same physiological state at the time of treatment. 

 At first several preliminary experiments were necessary in 

 order to determine the most suitable range of concentrations to 

 be used, since the time of exposures determined upon were brief, 

 the longest being ten minutes; in some cases of exposures only 

 three minutes were used. In this connection, the tables given 

 by Lillie 1 in his paper on the action of various anaesthetics in 

 suppressing cell-division in sea-urchin eggs, were exceedingly 

 helpful. For i-Amyl 2 alcohol, he finds 0.45 to 0.4 vol. per 

 cent, a favorable anaesthetic concentration for eggs subjected 

 for two and one half hours, while 0.5 vol. per cent, and above are 

 somewhat rapidly toxic. For Capryl 3 alcohol he finds the anaes- 

 thetizing concentrations to range between 0.012 and 0.02, and 

 notes that even in sub-anaesthetic concentrations this alcohol 

 exhibits a relatively high specific toxicity. With the help of 

 these data, and also Fiihner's 4 observations showing that in a 

 series of monohydric aliphatic alcohols each member of the group 

 is from three to four times as effective (for equimolecular con- 

 centrations) 5 as its immediate predecessor, it became a compara- 



1 R. S. Lillie, Journ. Biolog. Chem., 1914, Vol. 17, No. 2, pp. 129-139. 



2 Cf. reference just cited; Table VIII., p. 135. 



3 Cf. reference just cited; Table IX., p. 137. 



4 H. Fuhner, Arch. f. exp. Path. u. Pharm., 1904, LII., p. 69. 



6 Capryl alcohol used in exposures of five minutes seemed not to obey this 

 general rule, since in practically all experiments it was used in concentrations 

 nearly three times its computed strength. (See p. 137.) 



