THE PRODUCTION OF GRAFTED EMBRYOS. 77 



slowly or more quickly than its control, but taken altogether the 

 rate of development was clearly unaffected by the shaking; and 

 irregular development was absent, except for the larger number 

 of small atypic blastulse and gastrulse arising from the sloughed 

 off small extra-ovates. 



CENTRIFUGED EGGS. 



When fertilized eggs were centrifuged with or without previous 

 removal of the fertilization membranes, the normality of develop- 

 ment depended upon the centrifugal power employed. In 

 Table II., the effect of centrifugalizing from 35 to 90 revolutions 

 per minute, and from I to 15 minutes duration, is shown. 1 When 

 centrifuged at the rate of 35 revolutions per minute for ^2 to 7/4 

 minutes (in one experiment for 10 minutes), the subsequent 

 development was normal. When centrifuged 60 or more revo- 

 lutions a minute for even I minute considerable numbers of eggs 

 developed but very atypically. When centrifuged for longer 

 periods at this rate, the entire culture was rendered abnormal. 

 At 90 revolutions a minute the embryos were nearly all atypic 

 even though centrifuged ^ to I minute. Beyond this rate, or 

 for longer periods of time, the eggs were either killed outright or 

 broken into small fragments, only some of which developed into 

 the atypic blastulse or atypic gastrulse already mentioned. These 

 facts are shown in tabular form in Table II. 



TABLE II. 



Fertilized eggs were centrifuged at different rates and for varying periods of 

 time. Within well-defined limits of speed and time the embryos and larvae were 

 quite normal. 



No. Experiment. Result. 



ioe Centrifuged and shaken for 24 minutes. Few alive. Developed to young 



plutei only. 



20-1 Centrifuged 35 X per min. for 6 min. Developed to gastrulae only. 



8 Developed to gastrulse only. 



10 Developed to gastrulae only. 



I2J4 Developed to gastrulae only. 



15 Developed to blastulae only. 



Irregular. 



2$c Centrifuged 35 X per min. for i Developed normally. 



3 Developed normally. 



5 Developed normally. 



8 Developed irregularly. 



1 The arms of the centrifuge measured 150 mm. each. 



