The Origin of the Markings of Caterpillars. 225 



species in the fourth stage, and Niccza in the 

 third stage of its ontogeny. 



Although our knowledge of the history of the 

 development of the individual species is still so 

 fragmentary, we may conclude with certainty that 

 the development of the markings has been uniform 

 throughout that it has proceeded in the same 

 manner in all species. All the species appear to 

 be making for the same goal, and the question 

 thus arises whether there may not be an innate 

 force urging their phyletic development. The 

 rigorous examination of this conception must be 

 reserved for a later section. Here, as we are only 

 occupied essentially in establishing facts, it must 

 be remarked that retrogression has never been 

 observed. The young larval forms of a species 

 never show the markings of a later phyletic stage 

 than the older larval forms ; the development takes 

 the same course in all species, only making a 

 greater advance in the same direction in some 

 than in others. 



Thus, Niccza and Euphorbia have advanced to 

 the seventh phyletic stage, Zygophylli and Hippo- 

 phaes only to the third, and some specimens of 

 Zygophylli to the fourth. But at whatever 

 phyletic stage the ontogeny of a species may 

 terminate, the young larval stages always display 

 the older phyletic stages. Thus, Galii in its last 

 ontogenetic stage reaches the sixth phyletic stage ; 

 in its penultimate stage it reaches the fifth 



Q 



