ON EGGS OF MARINE ANIMALS 25 



which the worker may have some difficulty detecting. They can, 

 however, be found with ease in the later stages of development. 



Echinarachnius does not stand up well under adverse treat- 

 ment. One should therefore be sure that one has animals in 

 prime condition. Fortunately, this is readily ascertained. 



The normal intact animal is brownish red and discharges no 

 color into the sea-water. If the animal be injured locally the 

 point of injury becomes green, and the sea-water above it also. 

 One may prove this by scraping a part of the test of an animal in 

 perfect condition. Very quickly as the alkaline sea-water pene- 

 trates, the injured spot turns green. If one pours on to an intact 

 animal of normal color N/io NaOH, it turns green, but if one 

 uses N/io NHOH instead, the animal takes on a purple hue. 

 Only animals of the normal color should be used. I find that 

 the red pigment in the egg is also a natural indicator. (For 

 color indicators in other echinid eggs see Crozier, 1916.) 



The animals are best kept on a clean concrete sea-water 

 table. Though I have used Echinarachnius through August, I 

 prefer to work on them earlier because then they come to the 

 laboratory in better condition. This is largely due to tempera- 

 ture; the animals are not at their best when crowded in the tubs 

 after having been dredged from deep water during warmer days. 

 This is shown by the rapidity with which the sea-water in the 

 tubs is charged with the green color. At all times freshly col- 

 lected animals, properly cared for after collection, are best. 



I have frequently obtained Echinarachnius eggs normally 

 shed. As in the case of Arbacia the shedding may be induced 

 by injury — cutting the lantern or around the margin of the 

 animal. For obtaining eggs of optimum fertilization capacity 

 from the ovaries, these directions should be followed: 



Cut around the margin of the animal, remove and discard 

 oral portion. Place aboral portion (with the outside down) in a 

 clean, dry, Syracuse watch-glass. If the animal is ripe, sperm 

 (or eggs) will ooze from the gonads. Allow an opened male to 

 remain until you are ready for insemination. From the female 

 very carefully pipette off the eggs to 200 cc. of clean sea-water. 

 The sea-water in which the eggs are suspended should be clear 

 and not opalescent or milky through the presence of perivisceral 



