ON EGGS OF MARINE ANIMALS 17 



about by evaporation. Dishes containing eggs should be kept 

 covered. More than once results have been reported as due to 

 an experimental treatment which actually were brought about 

 by evaporation of the sea-water containing the eggs. I have 

 called attention to such cases. Two such alleged effects I have 

 disproved. (Just, 1928a; 1929.) 



Seasonal Changes 



When we speak of the breeding season, we do not mean that 

 the gametes are in exactly the same condition throughout this 

 season. For every animal there is variation during its breeding 

 season with respect to the quantity and to the quality of its 

 sexual products. For example: during the period in which one 

 can obtain ripe eggs and sperm from various heteronereids, 

 there is a time when the eggs and sperm can be obtained in 

 maximum abundance. At Woods Hole, the heteronereid form 

 of Nereis limhata appears at the beginning of the breeding season 

 in small numbers, which later rise, then taper off, so that in 

 September the number of animals captured is very small. The 

 quality of the gametes of this worm, however, remains the same, 

 as has been mentioned above. In other forms, as echinids, the 

 sexual products vary also in quality. At the beginning of the 

 breeding season of any named echinid the number of fully 

 matured eggs is small. This number increases as the season 

 progresses. There comes an optimum period when the eggs and 

 sperm are qualitatively in best condition. This is followed by a 

 period during which the gametes are of poorer quality. In this 

 time the eggs are not so amenable to experimental treatment. 

 Many so-called over-ripe eggs are now obtained which often 

 fail to fertilize. (Just, 1922a.) The worker in experimental 

 embryology, therefore, would do well to know these seasonal 

 variations and to plan his experiments accordingly. For any 

 named species, the breeding season varies with the locality. 

 For example, at Roscoff the breeding season for Strongylocen- 

 trotus lividus extends farther into the summer than at Naples 



To many a worker who has obtained results in default of 

 following these simple directions, I may seem to be pedantic 



