DEVELOPMENT OF EGGS <>F ARBACIA AND CH^TOPTERT -. 277 



hut the stronger solutions \vry soon proved toxic and greatly 

 retarded development. None of the eggs in the 2 per cent, solu- 

 tion of leucin had developed beyond tin- 2-cell stage at the time 

 ill, it the great majority of the eggs in all of the other solution-, 

 as well as in the control, were in tin- S-cell >tage. A solution of 

 this strength, however, does not kill the eggs quickly, a- twenty 

 hours after the experiment began this culture contained a few 

 i iliaied larva? that were much -mailer, and le active, than those 

 of the control lot. Within t\\ent\ -four hour- all of the laf\,e 

 in the 2 per cent, solution of leucin were dead. 



A microscopic examination \\a- made of a large number of 

 eggs taken from the 2 per cent, solution of leucin at different 

 stages in their development. Manv of the youiu eggs uere 

 abnormal in that there was an irregular di-t ribnt ion of the chro- 

 mosomes to the poles of the segmentation-spindle or a very un- 

 equal division of the blastomeres. Such abnormal eggs e\ identlv 

 died before reaching the bla-tulu stage, as nearly .ill of the older 

 embryos that were examined were normal although -OHM -\\liat 

 Miialler than those of the control culture. A fe\\ al'iiormal 

 Ma-tula- were found among the older larx.e. but a- tin --e Iar\.e 

 showed only such irregularities of form a> may be Imind in 

 individuals of almost every control culiure of Ar/xniti lar\a- 

 developing in a small amount of sea-\\ater under laboratory 

 (onditions, they could not be considered a- due to the ^p- ( itic 

 ai tion ol the leucin in changing the course ol de\ elopment . 



The eggs in the I per cent. >< 'hit ii >\\ < >\ leucin 1 u-gan to -In >\v t he 

 iniurious effects of the solution after the !ir>t hour, and from 

 tin- time on their development, although normal, lagged behind 

 that of the control: the weaker -olutioii- had apparently no 

 effects on the early segmentation. The bl.iMnl.e in the control 

 culture began moving about lilteen minute- -ooiu-r than the 

 lat \ a- in the other culture-, so e\ idcntly all of the leu< in -ohnioii- 

 retarded development some\\hat after the lir-t tu< or three 

 hour-. Pltitei that seemed perfectly normal, and that li\cd for 

 several days, dexeloped in all of the \\caker -olution-. An 

 examination of a considerable number of the-e embr\o-, pre- 

 -ei\ed at \arion- -tage- in their development, tailed to >ho\\ any 

 la i \ .e that \\ere in an\ \\a\ coni|>arable to the unu>ual t \ pe- that 

 Matin \\- obtained with impure leucin. 



