EMBRYOLOGY OF ECHINODERMS. 101 



Place a drop of fluid from the testis of this male upon a 

 clean slide, cover it with a cover glass, and examining it 

 with a power of two hundred and fifty to five hundred 

 diameters, notice that each spermatozoon consists of a 

 small, highly refractive, rounded "head," and a long, 

 slender, undulating "tail," and is somewhat tadpole-shaped. 

 If, with this power, the spermatozoa appear uniform in 

 size, and if there is httle or no fine granular matter scat- 

 tered among them, the fluid is probably ripe. 



Carefully cut out the reproductive organs of the male 

 which has been selected, and placing them in a large 

 watch-crystal, chop them up with a pair of scissors, to 

 facilitate the escape of the spermatozoa. Pick out and 

 throw away the fragments, and pour or wash the milky 

 fluid into a small tumbler or beaker, with about half a 

 pint of fresh sea-water. 



Set this aside, and chop up in the same way the ovaries 

 of the female which has been selected. Pick out the 

 fragments, and pour the red fluid into the water which 

 contains the spermatozoa, and having gently stirred it for 

 a minute or two, set it aside to allow the eggs to settle to 

 the bottom. 



In about half an hour, carefully pour or siphon off* the 

 water, replace it with fresh, and stir for a minute or two. 

 Repeat this process at the end of another half hour, 

 and so on until the water, after the earffs have settled, is 

 clear and transparent. Set it aside where it may have 

 plenty of light, without exposure to the sun. In about 

 twenty-four hours, the larvae which have hatched will be 

 found swimming close to the surface of the water. Care- 

 fully siphon them off, or draw them up with a dipping- 

 tube, and place them in another tumbler of water, in 

 order that they may not be poisoned by the decomposition. 



