THE MUTATION HYPOTHESIS 67 



It is very small, but is easily recognised by its elongated 

 form, its rapid jerky movements, and by the egg-sacs of 

 the female. It has numerous complicated appendages which 

 are used for locomotion, eating, catching prey, and various 

 other purposes. We may take Cyclops as a good example of 

 the free-swimming Eucopepoda, not the most complicated, 

 but not more highly differentiated in the way of appendages 

 than its fellows. In parasitic Eucopepoda, however, we find 

 forms such as Lesteira, where almost all appendages, organs, 

 and the general form are lost, excepting those connected with 

 digestion and reproduction. The beautiful antennules, the 

 legs, and other complicated appendages have disappeared, or 

 are present only as mere vestiges of the original structures. 



It is very advisable in considering whether or not muta- 

 tions are the groundwork on which new species have been 

 produced, that is, through which evolution has taken place, 

 to keep in mind the great differences existing between animals 

 and plants with regard to certain very important points, 

 bearing in mind also that de Vries has built his theory upon 

 observations in domesticated plants. In animals, that is, 

 in all animals excepting the lowest forms, variations can 

 apparently only take place upon the production of a new 

 individual. Plants may be propagated by grafts, cuttings, 

 and runners, without any throwing off or fusing of sexual 

 elements. In some cases even a portion of a leaf of the plant 

 when placed under suitable conditions will grow up into a 

 complete plant with all its organs and structures. Now it 

 appears quite legitimate to regard plants thus produced as 

 being in a sense all parts of the same individual. We will 

 take one example, the Lombardy poplar. Only one sex of 

 this tree exists, at any rate in Northern Europe. For several 

 hundred years all the Lombardy poplars have been produced 

 by cuttings ; they are therefore possibly actual portions of 

 the same individual. 



Variations, such as those that can only occur upon the 

 production of a new individual (using the term in the , 

 strictest sense) among animals, may occur among plants, not 



