THE AMERICAN NATURALIST [Vol. LV 



placed upon the precise value of the coincidence, it may be noted 

 that this amount, .7, is just what would be expected for a sim- 

 ilar distance in the X chromosome of Drosophila melanogaster 

 (ampelophila) . 



It should be noted here that Haldane, in referring to my re- 

 sults in a recent article, called attention to the fact that the 

 Primula data (using the counts of all classes of plants) fit his 

 formula for expressing the relations between linkage values in 

 Drosophila. Inasmuch as any formula expressing the linkage 

 relations in Drosophila is necessarily the mathematical resultant 

 of the operation of interference (interference of a type which 

 diminishes with increasing distance), Haldane 's statement that 

 the Primula data fit the same formula as Drosophila is equivalent 

 to saying that interference exists here, as in Drosophila ; it is in 

 this sense a restatement of my observation that the number of 

 double crossovers found in the total count of the plants is smaller 

 than the numiber "expected" in a case of a random occur- 

 rence of crossing over. It must further be noted that Haldane 's 

 formula for expressing the linkage relations in Primula is open 

 to the same objection of unreliability as noted above, since his 

 calculation is based upon all classes of plants, instead of upon 

 just those classes which I showed must be used in any reliable 

 determination. 



The finding of interference in another organism, so widely 

 separated from Drosophila, is of interest because of the bearing 

 of interference on the general theory of linkage. Interference 

 is not accounted for on Trow's form of the reduplication theory, 

 although it was the earlier experiments upon Primula itself 

 which largely supplied the data upon which this theory was 

 founded. 



Edgar Altenburg 



The Eice Institute, 

 Houston, Texas. 



ON INTERSEXES IN FIDDLER CRABS. 



Not long ago a few specimens of small female fiddler crabs, 

 Uca pugnax, were submitted to me by Professor T. H. Morgan 

 for determination. They appeared to be normal, immature in- 

 dividuals and I so stated in my reply. In order to demonstrate 

 the correctness of this view, a loan was made to Profe^r Mor- 

 gan from the National Museum collection of a series of imma- 



