32 BASIC METHODS FOR EXPERIMENTS 



animals in my experience tend to shed more readily. It is best, 

 therefore, to experiment on these eggs on the night of capture. 

 During the winter months, one can procure eggs and sperm by 

 rearing in the laboratory worms collected in the nereid phase. 



Chaetopter^is 



The sexes in Chaetopterus are distinguished by the color of the 

 sexual elements located in the parapodia; the eggs are orange- 

 colored, the sperm milky white. The sexes should be kept 

 separate, each individual being placed in a separate dish under 

 a gentle stream of sea-water. 



The eggs are removed by cutting the parapodia containing 

 them. The mucus present is removed by putting the eggs 

 through cheese-cloth. The eggs are then washed and set aside 

 for about fifteen minutes or until the first maturation figure in 

 the metaphase reaches the periphery of the egg. If not insemi- 

 nated, the eggs die in this stage. 



Sperm are obtained by removing a posterior parapodium 

 which is cut in lo cc. of sea-water. If a drop of the sperm- 

 suspension examinated under the microscope shows bundles of 

 nonmotile cells, spermatids, spermatocytes and spermatogones, 

 the animal is not ripe. Mature spermatozoa exude freely and 

 are highly motile. Insemination is made as for eggs of Nereis. 



Podarke 



Treadwell (1902) has used the eggs of this worm. He col- 

 lected them during the day and allowed them to spawn (at 

 night). I have seen several hundreds of these worms swimming 

 at the surface of the sea during Nereis runs. Because of their 

 small size they are hard to handle when taken at night, for they 

 are then shedding freely their eggs and sperm. If one wishes, 

 therefore, to study fertilization, one should collect the animals 

 during the day— from eel grass in the Eel Pond at Woods Hole. 



Amphitrite 



Amphitrite, which is very abundant in the Woods Hole 

 region, breeds "within two days of the new and full moon" 

 during the summer months. Shed eggs are always free from 

 admixture of coelomic corpuscles and unripe eggs. Every egg 



