T. M. SONNEBORN 169 



essary to inquire how extended each variety is in space and 

 whether potential gene flow exists within a variety. 



Distribution of the Varieties. About 260 collections of P. 

 aurelia from various parts of the world have been identified as 

 to variety in my laboratory and in the laboratories of Giese 

 (variety 16) and Beale. Most of these collections, about 200, 

 were made in the United States. Of the rest, most were collected 

 in Europe (chiefly by Beale), South America, and Japan. A few 

 were collected in India (5), Australia (4), Madagascar (1), 

 Puerto Rico ( 1 ) , and Hawaii ( 1 ) . Although the sampling is 

 spotty, unbalanced, and grossly inadequate, a few important 

 relations are clear (Beale, 1954; Sonneborn, 1956b). 



At least three of these varieties, 1, 2, and 6, are probably dis- 

 tributed around the world. Varieties 1 and 2 have been found 

 in Europe, North and South America, and Japan; variety 1 has 

 also been found in Australia and Hawaii. Variety 6 has been 

 found in the United States, in Puerto Rico, and in southern India. 

 It is rare in the United States, except in Florida; but all five col- 

 lections from the other two localities belong to this variety. In 

 addition to these three, variety 4 is also of wide distribution, 

 having been found in North and South America, Australia, and 

 Japan, but not yet in Europe. 



The other twelve varieties seem to be much less widely dis- 

 tributed. Variety 9 has been found only in Europe, variety 12 

 only in Madagascar, the other ten varieties only in the United 

 States. These statements need some qualification. Varieties 12, 

 13, 15 and 16 are large paramecia; until recently we have paid 

 little attention to paramecia of that size on the assumption that 

 they were not P. aurelia.'-* So we have only one collection of large 

 paramecia from outside the United States, and at present that 

 is our sole strain of variety 12. It would be premature to suggest 

 that 12 does not occur in the United States or that 13, 15, and 

 16 do not occur on other continents. However, even when these 

 three varieties of large paramecia are excluded, this leaves the 

 seven smaller varieties 3, 5, 7, 8, 10, 11, and 14 that have been 

 found only in the United States. If other parts of the world were 

 studied on a similar scale, it would not be surprising to find com- 



