DEPARTMENT OF MARINE BIOECXiY. 



147 



THE INFLUENCE OE CHANGES IN DENSITY. 



It was found that, depending upon the type of vessel and the quantity of 

 sea-water used, the evaporation varied as much as 50 per cent or more in 24 

 hours. In one experiment, for example, the evaporation after 24 hours was 

 as follows : 



Type of vessel and quan- 

 tities of sea-water (c.c). 



Finger bowls 



25 



50 



100 



200 



300 



Type of vessel and quan- 

 tities of sea-water (c.c). 



Finger bowls : 



400 



500 



Syracuse dishes 



20 



10 



Loss by 

 evaporat'n. 



p.ct. 

 10 



7 



44 

 40 



Density of 

 sea-water. 



I. II 



1.07 



1.78 

 1.66 



It was found that in concentrations to 1. 13 or 1. 14 either the variants were 

 not increased in number and kind or only slightly so. Beyond this concen- 

 tration, however, the plutei were increasingly irregular and atypic, though 

 of the same general type as those in control solutions. While the above 

 figures are not absolute, they do show that in finger-bowls ordinarily used in 

 this kind of experimental work not less than 200 c.c. of sea-water should be 

 used. With less volume the concentration due to evaporation under the con- 

 ditions of temperature and humidity at Tortugas was so great that the num- 

 ber of variants was greatly increased, the number and range depending upon 

 shallowness of dish, surface exposed, number of eggs, etc. 



In other experiments fertilized eggs were placed in sea-water whose den- 

 sities were changed either by addition of distilled water or by slow evapora- 

 tion to give the following series : 



0.60, 0.6s, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, i.oo, 1.05, I. II, 1. 17, 1.25, 1.33 



The number and types of variants and normal plutei found in normal sea- 

 water were likewise found in a wide range of solutions from 0.80 to i.ii. 

 Beyond these limits the number of variants increased with increasing changes 

 in density until 1.17 or 1.25 was reached on one side, and 0.75 or 0.70 on the 

 other. When the densities exceeded these limits the eggs rarely developed 

 into plutei, but most frequently died during cleavage. 



The Influence of CO2. 



The presence of CO2 was extremely injurious, whether its source was the 

 respiratory products of developing eggs or manufactured gas. The COg was 

 toxic even in small doses. Few or no eggs developed in sea-water contain- 

 ing more than 7.5 per cent carbonated sea-water. Development was retarded 

 or incomplete in solutions containing even 2.5 per cent of such carbonated 

 water. The plutei were irregular even in a i per cent solution, but these 

 irregularities were of the ordinary type. 



Overcrowding made for increased variation, and by suitable experiments 

 it was determined that for a volume of 200 c.c. of sea-water not more than 

 0.125 to 0.375 c.c. of eggs could be used, i. e., about 0.0006 to 0.0018 of the 

 entire volume, without introducing increased variability. In such numbers 

 the variants were reduced to a minimum. By increasing the number of eggs 

 or decreasing the volume of water the number of variants was correspond- 

 ingly increased. 



