I40 REVERSION AND ALLIED PHENOMENA 



The black polled Angus cattle form a well-marked breed, but 

 the progeny of a perfectly black polled bull and cow is some- 

 times a red calf with horns ; in all probability such a variation 

 is a true reversion traceable to some mixture of stocks a few 

 generations back. 



When the swimming-bell or medusoid Epenthesis folleata 

 appears with pentamerous symmetry instead of the usual 

 arrangement of its organs in fours or multiples of four, no one 

 would dream of calling this discontinuous variation an instance 

 of reversion, for we only know of one medusoid {Pseudoclytia 

 pentala) where five is normally the ruling number (Mayer, 1901). 

 But when the last-named medusoid occurs with four oral lips, 

 as it occasionally does, it may be said that this variation is 

 reversionary, since there is good reason to believe that Pseudo- 

 clytia pentata is a pentamerous derivative of the Epenthesis 

 stock. Even in this case the interpretation of the four lips 

 as reversionary may not be correct, since, as a matter of 

 fact, the number of lips in Pseudoclytia varies from one to 

 seven. 



ReYersion in Parthenogenesis. — Weismann (1893, p. 344) 

 reports a very interesting case which he observed in varieties 

 of a small Ostracod crustacean {Cypris reptans) which multiplies 

 parthenogenetically. In the course of observations extending 

 over eight years he found that, amidst the expected uniformity 

 of resemblance between parent and offspring, exceptions oc- 

 casionally occurred. These were of such a nature that he 

 could only interpret them " as exhibiting reversions to an 

 ancestral form many generations removed." 



White-flowering Currant. — The white-flowering variety of the 

 red-flowering currant [Ribes sanguineum) is said to have originated 

 many years ago from seed in Scotland. " Occasionally this white- 

 flowered currant reverts back to the original red type, and the 

 reversion takes place in the bud. . . Once reverted, the branches 

 remain for ever atavistic. It is a very curious sight, these small 



