STUDIES OF FERTILIZATION 429 
draws out the substance of the head of the spermatozo6n, which 
is very ductile at this time, into a strand, and in numerous cases 
it carries away the tail and middle piece or variable portions of the 
head in addition. Partial sperm heads of all sizes are therefore 
left attached to the egg by the perforatorium. Such partial 
sperm heads then penetrate, if the eggs be left to develop in sea- 
water, and their behavior may be studied. 
In each experiment 8 or 9 stages in the process of fertilization 
were centrifuged at five minute intervals, in order to be sure that 
the entire period of penetration of the spermatozo6n was covered, 
because particularly striking results were to be expected from 
removal of the external part of the spermatozo6n after a certain 
amount had entered (figs. 6 to 8). Several hundred eggs were 
centrifuged each time. One has to be sure that neither too little 
or too much centrifuging is done, and it was only as a result of 
considerable experience extending over three years that sixty 
revolutions of the handle of the centrifuge in about forty seconds, 
giving 7200 revolutions of the tubes at a radius of 6 em., was 
selected as most favorable. 
The following protocol of an experiment will show exactly how 
the experiments are carried out and the material secured for 
examination. 
EXPERIMENT 16 
September 21, 1911 
To preserve a series immediately after centrifuging and thirty minutes later 
Eggs fertilized at 8:28 a.m. Temperature of air, 18°C.; of water, 18°C. 
| 
OBSERVATIONS ON PER CENT 
DESIGNATION | CENTRIFUGING PRESERVATION lor SEGMENTED EGGS AMONG 
THOSE REMAINING 
a.m. | Ve karen: | a.m. | | a.m. 
Gis 1 eee < 60] 8:58 |16.1.1| 8:59 | 16.1.2| 9:29 -| 35 percent | 10.47 
os ae | X 60| 9:03 /16.2.1) 9:04 | 16.2.2] 9:34 | 15percent | 10.48 
Ga) ee X 60} 9:08 16.3.1) 9:09 16.3.2} 9:39 | 10 percent | 10.52 
GRA X 60/ 9:13 16.4.1| 9:14 | 16.4.2) 9:42 | Spercent | 10.54 
16552ee X 60| 9:18 /16.5.1) 9:19 | 16.5.2| 9:49 |25-80 percent] 10.55 
LG3O% 560) 9:28 6 NGeM 19:24 "|| 16162 Oras | 65 percent | 10.56 
1627 oA x 60| 9:28 |16.7.1| 9:29 16;7.2)) 9:58, |, 75 percent) 10.57 
1GRSMert X 60| 9:33 |16.8.1) 9:34.5 | 16.8.2) 11:03 | 85 percent | 11.02 
1G Ome X 60| 9:38 16.9.1 9:39.5 | 16.9.2 11:09.5 | 90+ percent | 11.03 
Controls—preserved at 8:57, 9:12.5, 9:35 A.M. .............. | 90+ per cent| 11.05 
