Gephyrea 199 



material to cover this period it is necessary to collect the animals in May 

 and keep them for rather long periods of time in the manner just de- 

 scribed. 



FERTILIZING THE EGGS 



Eggs or sperm may be removed from any of the six gonopores, which 

 lie in three pairs just posterior to the oral setae, by inserting into one of 

 these pores a finely drawn out pipette, which, of course, has been fire- 

 ended. Use one pipette for males and another for females to avoid 

 premature fertilization. Four or five hundred eggs should be placed in 

 a finger bowl and covered with % inch of filtered seawater, and then 

 fertilized by the introduction of sperm, at the same time mixing well by 

 squirting water in and out of the pipette. A minimum amount of sperm 

 for insuring fertilization should be used, as polyspermic conditions and 

 abnormal larvae nearly always result from an excess of sperm. 



CARE OF THE LARVAE 



These fertilized eggs should be covered and left to develop to the 

 trochophore stage, or from 18 to 24 hours. Then it is advisable to take 

 from these larvae those which are actively swimming near the surface 

 and distribute them to several finger bowls with approximately 50 to 

 each bowl. Remove any abnormal larvae whenever any are observed. 

 Put glass covers on the finger bowls and set them in a cool place. From 

 this time on the larvae should be carefully inspected and fed each day, 

 and changed to fresh filtered seawater about once each week. 



The above directions may need to be modified somewhat for the larvae 

 of other animals. 



It should be remembered that the length of the larval stage before 

 metamorphosis is not a criterion of what it would be under natural con- 

 ditions for obvious reasons. Since feeding must be carefully done to 

 prevent fouling, it is probable that the amount of food is quite different 

 from that of the open ocean. When raised in the above manner Urechis 

 larvae usually require from 40 to 60 days before they metamorphose 

 into burrowing worms. 



DIATOM CULTURES 



We have used several diatom cultures in the feeding of marine larvae, 

 but we are unable to give a technical name for any of the species used. 

 The first culture I used was one which I believe originally came from the 

 Plymouth Marine Laboratory, and which was already at the Hopkins 

 Marine Station of Stanford University when I first went there. Later I 

 cultured a single-celled green alga which grows quite abundantly on the 

 wet sand of the beaches. Later still a splendid form was cultured from 



