No. 584] HEREDITY AND ITS MEANING 477 



Neither chromosomes nor nucleus control, the size of the 

 cell in annelids, mollusks or ascidians. 



Relations between Chromosomes and External 

 Characters 



Thus there seems to be no constant relationship even 

 between nuclear or cell size and number of chromosomes, 

 and bonds of union between external taxonomic charac- 

 ters and chromosome number seem to be still more tenu- 

 ous. It is true tliat certain giant Primulas and (Enotheras 

 had more chromosomes than wore characteristic of the 

 normal forms, but it is just as clear that all giant Primulas 

 (and the same is probably true of (Enotheras, from the 

 work of Heribert-Nilsson and of Geerts) do not have ab- 

 normal chromosome numbers. 



Results on several species of both animals and plants 

 are interesting in this connection. 



The thread worm, Ascaris mcgalocepliala, has two va- 

 rieties, bi rale us and uiiiraleus, the former having as a 2N 

 number four chromosomes, the latter two chromosomes. 

 Nothing is known as to the origin of these two forms. 

 They are found parasitic in the same host individual and 

 neither form is rare. According to Herla, they hybridize 

 freely and produce embryos whose cells have three chro- 

 mosomes, but no mature hybrids have ever been found. 

 Meyer could distinguish no anatomical differences be- 

 tween the two varieties. 



Rosenberg investigated the reproductive structures of 

 two species of sundew and found one to have double the 

 chromosome number of the other. A subsequent com- 

 parison of anatomical and taxonomic characters failed to 

 show any sharply marked differences between them ex- 

 cept in size. The form having the smaller chromosome 

 number was smaller and less robust. They inhabit the 

 same territory and produce natural hybrids which are 

 sterile. 



nomic characters, but one form has thirty-four while the 



