An Introduction to a Biology 



characters have less tendency to be transmitted than old 

 ones. The case of snails will illustrate my meaning. In 

 Hdix nemoralis the unhanded condition is dominant over 

 the banded. Now, it is probable that some form of banding 

 is more ancient than colourlessness, and still more probable 

 that some form of colouring, at any rate, is more ancient than 

 colourlessness, yet absence of colour is dominant over colour. 

 But my point is that in crossing these snails the only thing 

 affected is colour ; this is almost true when H. nemoralis 

 is crossed with another species, H. hortensis : it is not quite 

 true, because the cast of the spire of the shell is also altered, 

 but the main thing which is affected is the colour. The 

 animal was a snail, a Helix, before it had any definite colour ; 

 and, even after it had become stamped as Helix, probably 

 underwent many alterations in coloration. I hold that it 

 cannot be denied that the characters with which one deals 

 are in this sense superficial. But I do not think that this need 

 be regarded as a damaging admission by the hybridiser. On 

 the contrary, I hold that the recognition of a limit between the 

 two sets of characters alterable and unalterable is desirable, 

 and that the discovery of the difference between the kinds of 

 characters which it separates would be intensely interesting. 

 The objection that the Mendelian only deals with hybridi- 

 sation phenomena doubtless very interesting and important 

 phenomena, it is often perhaps semi-ironically granted 

 must be met. Those who urge it complain : " It is all very 

 well to tell us about hybridisation about the result of the 

 union of unlike ; we want to know about the union of like. 

 Hybridisation seldom occurs in nature, and when it does the 

 results are more perplexing than in the case of crossing 

 domesticated breeds. What we want to know is, ' What 

 is the mechanism by which the similarity between parent and 

 son is brought about ? ' The existence of a form Triton 

 Blasii, which is a cross between T. marmoratus and T. cris- 

 tatus, is undoubtedly interesting, but it is an anomaly. I 

 want to know how it is that the offspring of the crested newt 



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