660 
DAVID H. TENNENT 
in glass vessels, heated in an enameled container to 65° C. filtered 
through paper and cooled. All dishes and utensils of whatever 
description were thoroughly boiled prior to being used. A dish 
once used was boiled before being used again. 
That there was an actual value in these precautions was demon- 
strated by the experience of other workers in the laboratory 
who were using less particular methods and were unable to keep 
Toxopneustes plutei alive. 
The plutei were kept in the finger-bowls, in some cases, as will 
be noted later, being fed from a diatom culture after the third 
day, in others kept until the seventh day without the addition 
of food. The loss of water by evaporation was restored by the 
addition of sterilized rain water day by day. 
By this method I was enabled to carry on a considerable num- 
ber, the number varying with different series, through their met- 
amorphosis, to the adult condition. 
By means of the precautions taken I was able to make fertili- 
zations and to keep the plutei alive throughout August, when by 
ordinary care in previous years the cultures were ruined by bac- 
teria. 
For work of the kind with which this paper deals, we need 
some standard method of treatment; a method which should be 
followed by every worker in the field. It is only by using uni- 
form methods that we can hope to obtain results that may be cor- 
related. 
The elimination of every possible extraneous influence is desir- 
able. No matter how great the care taken, there are sufficient 
circumstances over which we have no control. We should adopt 
the simplest possible method; one which may be applied with 
equal facility to straight fertilizations or to cross fertilizations. 
When the embrj/os were withdrawn for measurement the con- 
tents of the dish were thoroughly stirred up, a portion of the water 
dipped out and the embryos in this portion thrown down by the 
addition of fresh water. Sufficient alcohol to preserve the em- 
bryos was then added and the measurements made as soon as 
possible. By this method distortion in form was avoided. Care 
must be taken that the alcohol be free from acid. 
