140 Experimental Zoology 



viduals may be designated by ^^ and the bandless by - 



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The young of the first generation are all without bands. In other 

 words, the banded condition is the recessive. The formula used 



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by Lang for these individuals is - 



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When the individuals of the first generation (F^ are paired, the 

 offspring of the second generation are of two sorts (like the grand- 

 parents). Those having the dominating character (bandless) 

 are to those with bands as 3 to i . In other words, the Mendelian 

 ratio appears. That this is really the case is shown by further 



experiments. The banded individuals are the recessives, - > 



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and produce only banded offspring. The bandless are of two 



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kinds, one third true or "pure" dominants, > and two 



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thirds dominant recessives, . There are no external char- 



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acters that distinguish the pure dominants from the dominant 

 recessives, since both are bandless ; but if they are separated in 

 pairs and their offspring obtained, it will be found that in some 

 cases all of the offspring will be bandless. They have arisen 



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by the union of two extracted dominants, - x , or by 



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the union of one extracted dominant and of one dominant reces. 



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sive, - x - .In other cases two thirds of the offspring 

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are bandless and one third banded, showing that two dominant 



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recessives have paired, - x 

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Lang has also carried out some experiments with snails in 

 which two characters are involved. The individuals of Helix 

 nemoralis or of H. hortensis differ not only in their banding but 

 also in the color of the shell, which may be yellow or red. These 

 colors also form a pair of antagonists that follow the Mendelian 

 law. The double combination of banded and bandless, yellow 

 and red, gives the Mendelian expectation for two contrasted 

 characters. 



