THE METHOD OF ORGANIC EVOLUTION 357 



Discontimwtis Variations. 



It thus appears that what is evidently supposed to be 

 a very powerful argument leading to the conclusion that 

 discontinuous variations as a class are those which are of 

 vital, if not exclusive importance in the production of new 

 species, entirely breaks down when confronted with the 

 facts of nature. It does not, however, follow that, because 

 an unsound a priori argument has been used to call atten- 

 tion to these variations, and because they have been set 

 before the world in a way to suggest that their importance 

 in relation to the origin of species is a new discovery 

 calculated to revolutionise the study of this branch of 

 biology, they are, therefore, of no value in this connection. 

 We will, therefore, now proceed to consider them on 

 their own merits as possible factors in the process of or- 

 ganic evolution. For this purpose we must briefly indicate 

 the nature of the variations so laboriously recorded in 

 this volume. 



' These consist of what are termed meristic variations, 

 that is, variations in the number or position of parts 

 which occur in series, whether linear, bilateral, or radial. 

 Such are the variation in the number of segments of annu- 

 losa and arthropoda, such as worms, leeches, centipedes, 

 &c. ; in the antennae and legs of insects ; in the vertebrae, 

 ribs, teeth, nipples, limbs, and toes of vertebrates; in the 

 rays of starfish, encrinites, and allied animals. The ocelli 

 and other symmetrical markings on the wings of butterflies 

 are also recorded, as well as numerous malformations when 

 these affect serial or symmetrical organs. 



On carefully looking through the cases of variation in 

 this volume we are struck with the large proportion of 

 them which exhibit more or less deformation or want of 

 symmetry, culminating in the various kinds of monstrosity. 

 In Chapter III., on the variations of vertebrae and ribs, 

 we find vertebrae imperfectly divided in snakes and frogs. 

 Numerous cases of abnormalities in human vertebrae are 

 given, usually exhibiting asymmetry or deformation, and 

 similar variations are found in the anthropoid apes, but 



