544 Phylum Mollusca 



sirable to use them the day they are collected, although it is sometimes 

 possible to keep them for a day or two in moist sand. They must be 

 kept away from water if it is desirable to have them retain their eggs or 

 sperm. 



CULTURE METHODS 



By the procedure just described eggs and sperm are spawned in sep- 

 arate dishes and the eggs may be kept several hours without fertilization. 

 Before insemination it is good practice to change the water on the 

 eggs and then add one or two drops of sperm. Polyspermy occurs if 

 too much sperm is used. The fertilized egg develops into a swimming 

 gastrula in a few hours. In the meantime it is desirable to change the 

 water on the cleaving eggs two or three times to get rid of excess sperm 

 and body fluids. After 12 hours all of the normal embryos, which have 

 now reached the trochophore stage, are swimming near the surface of 

 the water and may be poured into a fresh dish of seawater, leaving behind 

 the debris and eggs which failed to develop. This process should be 

 repeated once more within the next three or four hours and then the 

 embryos may safely be left to develop undisturbed for a day or two 

 without further care. 



Under moderate summer temperatures the trochophores begin to show 

 development of the bivalve shell within 18 or 20 hours and within 30 

 hours they become swimming veligers with bivalve shell covering the 

 entire body. After the embryos (veligers) are two days old they have 

 a tendency to settle to the bottom and lie quiescent. When this occurs 

 they may easily be transferred to fresh dishes of seawater by means of 

 a pipette. This change should be repeated daily as long as it is desired 

 to keep the embryos. They remain veliger larvae, with no evident 

 change in structure except increase in size, for three weeks. In the 

 meantime they must be fed upon diatoms, preferably a pure culture. 

 [See p. 36.] After a period of three or four weeks of successful cultur- 

 ing they lose the velum, metamorphose, and take on the form of the 

 adult. This metamorphosis has been successfully accomplished in the 

 laboratory at Woods Hole by keeping the veligers in a 4-gallon cylin- 

 drical aquarium jar in which a stirring device was installed, keeping the 

 water agitated once per minute. The embryos were fed upon a pure 

 culture of diatoms which was isolated at the Plymouth laboratory. It 

 would no doubt be possible to carry them through metamorphosis in 

 small dishes without aerating devices. 



Bibliography 



Grave, B. H. 1927. The natural history of Cumingia tellinoides. Biol. Bull. 

 53:208. 



