178 PROTOZOOLOGY 



acters. To the last-mentioned category belongs perhaps a strain of 

 Tetrahymena geleii in which, according to Fiirgason (1940), a pure- 

 line bacteria-free culture derived from a single individual was found 

 to be composed of individuals differing in shape and size which be- 

 came more marked in older cultures. 



The first comprehensive study dealing with the variation in size 

 and its inheritance in uniparental or vegetative reproduction of 



Table 7. — Relation between the number of days cultivated in peptone 

 medium and the number of days \cultivated in salt-sugar medium needed to 

 change from type\l tojype 5\in Chlamydomonas]debaryana (^Moewus). 



Protozoa was conducted by Jennings (1909). From a "wild" lot of 

 Paramecium caudaium, eight races or biotypes with the relative 

 mean lengths of 206, 200, 194, 176, 142, 125, 100, and 45/i were 

 isolated. It was found that within each clone derived from a single 

 parent, the size of individuals varies greatly (which is attributable to 

 growth, amount of food, and other environmental conditions), any 

 one of which may give rise to progenj^ of the same mean size. Thus 

 selection within the pure race has no effect on the size, and the differ- 

 ences brought about merely by environment are not inherited. Jen- 

 nings (1916) examined the inheritance of the size and number of 

 spines, size of shell, diameter of mouth, and size and number of 

 teeth of the testacean Difflugia coro/m, and showed that "a popula- 

 tion consists of many hereditarily diverse stocks, and a single stock, 

 derived from a single progenitor, gradually differentiates into such 

 hereditarily diverse stocks, so that by selection marked results are 

 produced." Root (1918) with Centropyxis aculeata, Hegner (1919) 

 with Arcella dentata, and Reynolds (1924) with A. polypora, ob- 

 tained similar results. Jennings (1937) studied the inheritance of 

 teeth in Difflugia corona in normal fission and by altering through 



