AND OF SALINITY. 



279 



generation was more than twice as fast as in normal 

 water, but with further dilution it rajpidly diminished, 

 and ceased altogether in water of Sp. Gr. 1.013. 



Somewhat similar results to these were obtained by 

 the author for sea-urchin plutei. As we saw in the 

 last chapter, the actual size of an organism is probably 

 affected by environment in a similar manner to the 

 growth rate, and the author found that these plutei, 



1.02 



Dilute Sea Water 



Concentrated Sea Water 



Specific Gravity 

 FIG. 24. Effect of salinity on growth of Tubularia. 



allowed to develop in sea-water of various concentra- 

 tions, attained a greater size than the normal when kept 

 in moderately diluted water, and probably a slightly 

 smaller size when kept in concentrated water. The 

 results obtained are indicated in the subjoined figure, 

 where the abscissae represent the salinity of the 

 water, and the ordinates the average percent- 

 age variation in the size of the larvae after eight 

 days' growth, as compared with that of larvae grown 

 in normal sea-water. The salinity of normal water 

 was taken as 1000, and the less saline waters were 



* Phil. Trans. 1895, B. p. 586. 



