1 88 Phylum Annelida 



OBTAINING EGGS AND SPERM 



Uninjured animals are most easily obtained using the following pro- 

 cedure: (i) remove the sand tube from the shell or rock, (2) break 

 away enough of the tube to make the head and tail visible within, 

 (3) carefully force the animal from the tube by inserting a blunt probe 

 into the head end of the tube. 



The sex of the animal removed from the tube is ascertained, if the 

 color of the abdominal segments is not definitely white or pink, by 

 placing it in a few drops of seawater until it begins to shed. The sperm 

 usually pour out of the male in dense white clouds. The masses of eggs 

 shed by the female break up in the water into small groups. The male is 

 placed into four drops of seawater until it has completed shedding. The 

 female is placed into a finger bowl containing about 200 cc. of clear sea- 

 water. After it has shed for a few seconds, it is moved to a new position 

 in the finger bowl and allowed to shed in that place for the desired length 

 of time, depending on the number and kind of eggs desired. The first 

 eggs to be shed are not generally used because of the possibility of their 

 having been on the surface of the animal while exposed to the air. 



When preparing the eggs for fertilization, it is best to allow them to 

 remain in the seawater for about fifteen minutes. Towards the end of 

 that time, the sperm suspension is prepared. One drop of the sperm shed 

 into the four drops of seawater is diluted with four drops of seawater, 

 and one drop of this diluted suspension is then added to a finger bowl of 

 seawater (about 260 cc). The eggs are drawn up with a narrow medi- 

 cine dropper and transferred into this suspension.* 



The original sperm suspension (made by allowing the male to shed in 

 four drops of seawater) may still be used after three to four hours and 

 longer if evaporation of the water is prevented. The eggs may be 

 fertilized immediately after shedding, but it is best to allow them to 

 remain in the water for about fifteen minutes before they are fertilized, 

 if eggs of the same stage of development are desired. 



EARLY DEVELOPMENT 



Just after being shed, the egg is very irregular in shape and contains 

 a large clear germinal vesicle. A few minutes later, the egg begins to 

 round out, a clearly visible membrane is raised from the surface, and the 

 large germinal vesicle breaks down to form a spindle which extends across 

 not quite half the diameter of the egg. The average diameter of the 



* This procedure is quite different from that of Waterman (1934) who placed the male 

 and female together in a finger bowl of seawater. The method used by me has the fol- 

 lowing advantages: 1 — The eggs obtained are more nearly alike with respect to the stage 

 of development. 2 — The eggs are obtained free from the debris which clings to the bodies 

 of the animals. 3 — The use of the small quantity of sperm gives higher percentages of 

 normal development. Polyspermy, which might otherwise be encountered, is avoided. 



