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THE AMERICAN NATURALIST [Vol. XLIX 



important, in considering these experiments, to note that 

 two sets of similar chromosomes are present in a normal 

 sexually produced organism. 



Pairs of chromosomes of each shape and size (if they 

 differ in shape and size) are nearly always found in the 

 somatic cells — the exception being , when the so-called 

 accessory chromosomes are present. And since but one 

 of each kind is found in the two gametes that fuse to form 

 the new organism, it is only natural to suppose that one 

 set was contributed by the maternal parent and the other 

 by the paternal parent. 



The numerous cases in which this phenomenon has been 

 demonstrated are to many the most convincing evidence 

 of some sort of a morphological individuality of the chro- 

 mosomes. To them the fact implies pairs of freight boats 

 loaded with the essential materials of life, to others— the 

 minority— it is no more wonderful than the constant re- 

 currence of other plant organs. At any rate, it has been 

 shown that these sets of chromosomes continue an appar- 

 ently independent existence for some time. Moenkhaus 

 produced hybrids between the two species of fish, Fundu- 

 lus heteroclitus with long straight chromosomes and 

 Menidia notata with short curved chromosomes, and the 

 early divisions of the fertilized egg showed clearly com- 

 plete sets of chromosomes from each parent. Rosenberg 

 obtained similar results in crosses between the two sun- 

 dews, Drosera longifolia, which has forty small chromo- 

 somes, and Drosera rotund) folia, which has twenty large 

 chromosomes. In some cases similar to the latter, where 

 one parent contributes a greater number of chromosomes, 

 it should be noted that the organism seems to have regula- 

 tory powers. The chromosomes unnecessary for a double 

 set are either thrown out or take no part in the activities 

 of cell division. For example, in the supposedly hybrid 

 sundew, Drosera ohovatn, Rosenberg found that its thirty 

 chromosomes behaved in the following peculiar manner. 

 Ten of them paired with another ten, but the other ten 

 remained unpaired and acted in a very abnormal fashion 



