Water 



15 



When transferred from 100 per cent to dilute sea water, the weight of N. 

 diversicolor rises to a maximum and then, in contrast to N. cultrifcra, falls in 

 20 hours to a steady level, slightly higher than its weight in normal sea water 

 (Fig. 5, curve C)-"'' "''^ The concentration of body fluids follows a curve 

 inverse to the weight curve (Fig. 5, curve A), but the body Huids remain more 

 concentrated than the dilute medium. Specimens have been kept for two 

 weeks in good condition in fresh water. -'•'* Figure 6 shows that N. diversi- 

 color, in contrast to N. pelagica, remains hypertonic in dilute sea water but is 

 unable to maintain the same concentration in a dilute medium that it had in 

 normal sea water. Its concentration curve steadily declines on tbe dilute side, 

 i.e., it does not flatten as does the curve of very successfully regulating animals. 

 In order to carrv out active osmoregulation, work must be done. Schlieper 



5 10 



TIME IN bO'X SEA WATER 



HOURS 



Fig 5 Weight changes observed (curve C) and calculated as it there were no salt 

 loss or excretion (curve B); body fluid concentration (curve A); in Nerds chverstcolor 

 in 50 per cent sea water from zero hours. From Beadle."" 



213 observed an increase of 8 to 17 per cent in oxygen consumption of N. 

 diversicolor in dilute sea water, but after an hour the oxygen consumption was 

 reduced Beadle--^- -'^ attributed the initial increase in respiration rate to 

 muscular resistance to swelling. However, in 0.001 M potassium cyanide or m 

 anaerobic conditions, osmotic regulation breaks doun and the weight curve 

 approaches that of N. cidtrifera. , , ..- ,-.• t i 



Calcium is important in regulating salt intake and loss.-" " In normal 

 20 per cent sea water the weight initially increases, then recwers (Fig. /, 

 curve B), whereas in 20 per cent sea water free of calcium the worm remains 

 swollen (Fig 7 curve A). Also a worm which has become adjusted to normal 

 20 per cent sea water gains weight rapidly when transferred to sea water of 

 the same dilution but lacking calcium. No such water reabsoiTUon occurs 

 when the water lacks sodium, potassium, or magnesium. When a worm 



