26 BASIC METHODS FOR EXPERIMENTS 



fluid. Allow the eggs to settle. Pour ofi" the supernatant sea- 

 water and very carefully add sea-water up to the original volume 

 employed. Now strain the egg suspension through clean, 

 washed cheese-cloth wetted with sea-water. The eggs are now 

 ready for use. If the time consumed in opening the animal and 

 preparing the eggs amounts to more than one hour, open some 

 more animals until you get a good male, discarding the others, 

 in order to have perfectly fresh sperm. Inseminate the eggs as 

 you would those of Arbacia. 



Strongylocentrotus, Sphaerechinus, Echinus and Echinocardium 



Methods for Strongylocentrotus, Sphaerechinus and Echinus 

 are the same as those for Arhacia. 



For Echinocardium I proceed as follows: The fragile test is 

 opened carefully on the oral side and the portion of the test thus 

 cut is gently removed. If the eggs exude from the genital pores, 

 the animal is placed in a dry watch-glass. If, instead, the eggs 

 ooze from the ovaries, they are removed to clean sea-water. 

 Opened males are placed in dry watch-glasses and the sperm 

 pipetted off to sea-water to make up a sperm-suspension just 

 before insemination is planned. The egg of Echinocardium is 

 beautifully transparent and most favorable for observation 

 during development. The animal, however, is very fragile and 

 hence sensitive. It should be handled with utmost care. 



Asterias 



The eggs of Asterias forbesii, A. vulgaris and A. glacialis are 

 most beautiful for many purposes, when properly handled; 

 unfortunately they are greatly maligned by many workers. 

 This is not the fault of the egg. The first essential is to get good 

 animals with ripe gonads. 



Asterias forbesii and A. vulgaris 



When fully ripe the animals are heavy, their skin is soft and 

 their arms bulging. I .determine ripe animals by roughly 

 estimating their weight, rejecting the lighter ones with firm 

 brittle skin and narrow arms. Frequently, I have been able to 

 select the ripe animals so exactly that when using eggs only, 



