NO. 558] CLONAL VARIATION IN PECTIN ATELLA 371 



The difference between the members of the first pair 

 is chiefly in the scattering of the distribution — in the 

 variability — inside the colony. The difference between 

 the members of the second pair is a difference of mode — 

 of type. .These latter two distributions, and others in 

 Table VIII, have little in common ; they are the product 

 of distinct biotypes. 



Inside of a single biotype — inside of a single colony — 

 there is a great variability in the number of hooks. Why 

 is this? Unfortunately, we do not know. The query is 

 one with others concerning the cause of variability, upon 

 which we hope to shed some light. 



Our study suggests that the difference in the average 

 number of hooks in mid and late summer statoblasts is 

 not due merely to the differences of age, temperature and 

 food conditions in these two seasons, but probably also 

 to the circumstance that the biotype that forms many 

 hooks is one that develops later in the season than the 

 others. Our study has, indeed, solved few problems, it 

 has rather shown what a fine field for investigation is 

 offered by the remarkable variation of the hooks on the 

 statoblasts of Pectinatella. 



Cold Spring Harbor, N. Y., 

 February 25, 1913 



LITERATURE CITED 

 Braem, F. 1911. Die Variation bei den Statoblasten von Pectinatella 



magnifica. Arch. f. Entw. Mech. der Organismen, XXXII, 314-348. 

 Braem, F. 1912. Nachtraglicb.es iiber die Variation der Statoblasten von 



Pectinatella. Arch. f. Entw. Mech. der Organismen, XXXV, 46-55, 



Oct. 



Davenport, C. B. 1900. On the Variation of the Statoblasts of Pectinatella 

 magnifica from Lake Michigan at Chicago. Amer. Nat., XXXIV, 

 959-968. 



