96 CORRELATED VARIATIONS. 



Analogous or Parallel Variation. This term has 

 been used by Darwin to indicate that similar characters 



i/ 



occasionally make their appearance in several varieties 

 or races descended from the same species, and more 

 rarely in the offspring of widely distinct species.* It 

 is unnecessary to make more than very brief mention of 

 this subject, because, as Darwin points out, the majority 

 of observed cases such as the occasional appearance of 

 black wing bars in the various breeds of pigeon, and of 

 stripes on the legs of the ass and of various races of the 

 horse are evidently due to reversion. The others are 

 probably mere coincidences, and of no scientific value. 

 Among these latter, Darwin mentions the fact that 

 many trees belonging to quite different orders have pro- 

 duced pendulous and f astigate varieties. A multitude 

 of plants have yielded varieties with deeply cut leaves. 

 Several varieties of melon resemble other species in im- 

 portant characters. Thus one variety has fruit so like, 

 both externally and internally, the fruit of the cucum- 

 ber, as hardly to be distinguished from it. In animals, 

 again, we find feather-footed races of the fowl, pigeon, 

 and canary bird. Horses of the most different races 

 present the same range of colour. Many sub-varieties 

 of the pigeon have reversed and somewhat lengthened 

 feathers on the back parts of the head. 



In connection with this subject of parallel variation, 

 Walsh's " Law of Equable Variability " f may be men- 

 tioned. This states that " if any given character is 

 very variable in one species of a group, it will tend to 

 be variable in allied species ; and if any given character 



* " Animals and Plants," vol. ii. p. 340. 



f Proc. Entomolog. Soc. Philadelphia, p. 213, 1863. 



