126 TELEGONY AND REVERSION. 



o£ necessity result in what might be termed retrogressive 

 changes — result in something more than mere arrest in 

 development. The cx-ossing of two distinct varieties or of 

 two well-marked species might very well be expected to 

 result in an intermediate form ; but owing to the antago- 

 nism between the units of germ-plasm derived from two 

 dissimilar individuals, it is undoubtedly to many all but 

 inconceivable that crossbred progeny should possess in an 

 exaggerated form the characters of either of the immediate 

 ancestors. We might a 'priori as well expect a mixture 

 of red and blue sand to be intensely red or intensely blue 

 rather than purple. 



Nevertheless, the numerous stripes across the face and 

 body of Romulus and the spots over the hind quarters 

 may after all be due to discontinuous variation. Hence 

 although Darwin was wont to ascribe to reversion the 

 appearance of transitory stripes on foals, and the more 

 permanent stripes on mules, it will be well to consider 

 whether the zebra hybrids do not in their coloration 

 aiford a striking instance of discontinuous variation. 

 Bateson in his suggestive work on variation says, " Around 

 the term reversion a singular set of false ideas have gathered 

 themselves," and that '^ it would probably help the science 

 of biology if the word ' reversion ' and the ideas which it 

 denotes were wholly dropped, at all events until variation 

 has been studied much more fully than it has yet been.""^ 

 He also says that to adopt the reversion hypothesis to 

 explain the discontinuous occurrence of new forms possess- 

 ing much perfection and completeness is inadmissible, 

 because of the frequent occurrence by discontinuous varia- 

 tion of forms which, though equally perfect, cannot all be 

 ancestral. 



There is probably much truth in what Bateson says. 

 Keversion may have been credited with results which 

 could be sufficiently accounted for by variation. I have no 

 means of knowing whether Bateson and others who have 

 adversely criticised the reversion hypothesis, would account 

 * ' Materials for the Study of Variation,' 1894. 



