478 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



tion increases the breadth ; decrease of nutrition decreases it. The 

 response of breadth to changes in nutrition is immediate and very 

 marked. Within twenty- four hours increased nutrition caused in 

 the D hne an increase of 49.724 per cent, in breadth (rows 8 and 9, 

 Table XVIII.) ; in the c hne it caused in twenty- four hours an 

 increase of 40.778 per cent, (rows 17 and 19, Table XVIII. ). 



But the decrease of breadth with decrease of nutrition does not 

 vary directly with the time; when plump individuals are left without 

 food, they decrease much more rapidly at first than later. Thus, in 

 the series shown in Table XVIII., rows 2, 3 and 6, the breadth 

 decreased in the first forty-eight hours 21.324 microns, or 32.867 per 

 cent. ; in nine days more of lack of food the breadth decreased only 

 5.476 microns, or 8.440 per cent. more. 



Proportion of Breadth to Length. — Since changes in nutritional 

 and other conditions act more readily and more strongly on breadth 

 than on length, and since the same agent may increase the breadth 

 while decreasing the length, the proportion of breadth to length varies 

 greatly under different conditions. The mean index, or ratio of 

 breadth to length, varies in different cultures of the D line from 

 21.337 P^r cent, to 36.123 per cent.; in the c line from 23.067 per 

 cent, to 41.455 per cent. Since the breadth is more dependent on 

 nutritive conditions than is the length, we find the lowest ratio of 

 breadth to length in the starving cultures (rows 8, 26, Table XVIII.) ; 

 the highest ratio in well-fed cultures (rows 2, 14, 19, Table XVIII. ). 

 An increase of nutrition causes uniformly an increase of the ratio 

 of breadth to length; a decrease of nutrition has almost uniformly 

 the reverse effect. A single exception to the relation last mentioned 

 is seen in the change from row 21 to row 22, Table XA'III. ; here 

 other causes, connected with conjugation, were probably at work. 

 Whenever the mean breadth increases, the mean ratio of breadth to 

 length likewise increases. (The only exception is the case just men- 

 tioned, where conjugation was involved.) It must be understood 

 that this does not mean that in all cases the mean ratio of breadth 

 to length varies directly with the mean breadth ; if we compare rows 

 6 and 7, Table XVIII. , for example, we find that this is not the 

 case. But whenever, as a matter of experimental procedure, the 

 mean breadth was caused to increase, the mean ratio of breadth to 



