560 • WALDO SHUMWAY 



11 after the expulsion of the large non-contractile vacuole. The 

 malformed individual divided at the same rate as other and more 

 normal thyroid treated sister cells and produced descendants 

 normal (for the thyroid line) in every respect. 



These vacuoles then are to be considered another evidence of 

 a greatly increased activity of the excretory system due to the 

 thjToid diet. 



e. On monstrosities. From my observations upon the three 

 races of Paramaecia here reported, I have become more and 

 more impressed with the remarkable variability of the Paramae- 

 cium morph, and its adaptivity to environmental changes, and 

 by the appearance of apparent "mutations" which have no 

 hereditary significance. The appearance of a Paramaecium 

 with an extra contractile vacuole would at first glance seem 

 almost important enough for the erection of a new species, yet 

 it has arisen in my cultures as the response to an increased 

 amount of excretion produced by thyroid feeding. 



The 'hooked' Paramaecium described above was maintained 

 in a sub-culture of thyroid medium where it lost its distinguish- 

 ing character after a few generations, thereafter, dividing at the 

 same rate as the other thyroid fed individuals and showing no 

 tendency to throw 'hooked' descendants. 



A third example may be mentioned. In the A race in one of 

 the thyroid treated lines a form appeared which was almost 

 spherical. Later observations showed that this tj^pe of indi- 

 vidual was due to a form of division in which the posterior cell 

 was twice as long as the anterior. Seven cases of this asymet- 

 rical mode of division are recorded in my notes. Four were es- 

 tablished as a sub-culture and treated with thyroid, three were 

 maintained in control medium. The latter died within twenty- 

 four hours. Those in the thyroid medium after a few divisions 

 producing cells like themselves regained the normal shape and 

 after being maintained a few generations longer without throw- 

 backs were abandoned. 



These cases are introduced out of many which have occurred 

 in the course of the experiments, in none of which have I seen 

 any evidence of any inheritance of the acquired character or 



