548 Phylum Echinodermata 



gametes the animal is rinsed in tap water to kill any sperm clinging to it, 

 and then rinsed again in seawater. The tip of one arm is cut off, and an 

 incision made along the aboral surface to the central disc, in order that 

 the plume-like gonads may be examined. Only if these fill a large portion 

 of the arm is the individual usable. A male is distinguished by whitish 

 or pale yellow gonads; those of the female are orange in color. Males 

 are laid aside to be used later. In the case of a female, the other arms 

 are cut as just described. The entire aboral surface of the disc, and of 

 each arm in the region near the disc, is removed, and the sides of the arms 

 are forced apart. Thus the entire animal is exposed aborally, and the 

 plumes are fully visible. Throughout these operations care is used not 

 to harm the ovaries or their gonoducts. 



The dissected specimen is rinsed to wash away the body fluid. Just 

 states (1928) that this fluid is deleterious to development, but the 

 writer's experience indicates that small traces do not affect development 

 adversely. Several experiments carried out with the aid of Miss Ann K. 

 Keltch show that maturation, fertilization, and cleavage are not modified 

 unless the concentration of body fluid is over 1%. 



The ovaries are transferred to a vessel containing about 1,000 cc. of 

 •water. With a forceps each one is picked up at the blunt end, near the 

 gonoduct. Since this is the region which contains the eggs ready to 

 develop, it is important that all of it be removed. The narrow end con- 

 tains oogonia; for this reason Just (1928) warns against cutting up the 

 ovaries. 



During development it is desirable that eggs pass through the various 

 stages simultaneously. Since they stream forth and begin to maturate 

 at once, the plumes should be transferred to the water as nearly at the 

 same time as possible, and removed in a few minutes. If the plumes are 

 allowed to shed their eggs over a long period there is a wide "spread" of 

 mitotic stages in the developing set of eggs. 



From some ovaries eggs gush out in large quantities. Those which 

 do not shed so freely should be gently shaken to aid the release of eggs. 

 Just (1928) warns against the harmful effects of overcrowding, but the 

 writer's experience indicates that crowding is harmful only if continued 

 for a relatively long time, and only if the seawater is unchanged. 



Since the specific gravity of Asterias eggs is only slightly greater 

 than that of seawater, they settle very slowly. Therefore it is important 

 that they be disturbed as little as possible while they are being shed from 

 the ovaries, because if they are thrown into suspension at that time it is 

 difficult to secure samples of adequate size for experimentation until 

 they have settled. After the plumes are removed, most of the seawater 

 is poured off, leaving the majority of the eggs in a relatively small amount 

 of water. Thus suitable samples are available for immediate experi- 



