The Origin of the Markings of Caterpillars. 227 



From this very incomplete table we perceive 

 that, in certain instances, the stages can be repre- 

 sented as a continuous series of phyletic steps, as 

 in the case of D. Galii ; that in others certain steps 

 may be omitted, as with D. Euphorbia, in which 

 grade I. of stage i is immediately followed by 

 grade V. in stage 2. In reality the gap caused 

 by this omission is still greater than would appear, 

 as grade V. is only indicated, and not actually 

 reached, the subdorsal not being present as a 

 sharply-defined line, but only as a faint stripe. 

 The suppression of phyletic steps increases with 

 the advancement in phyletic development. The 

 higher the step to which a species finally attains, 

 the greater is the tendency of the initial stages to 

 be compressed, or omitted altogether. 



From what has thus far been seen with respect 

 to the development of D. Hippophaes, there may 

 be drawn what to me appears to be a very 

 important conclusion, viz. that the ring-spots 

 of Deilephila first originated on the segment 

 bearing the caudal horn, and were then gradually 

 transferred as secondary spots to the preceding 

 segments. Complete certainty would be given to 

 this conclusion by a knowledge of the young 

 forms of other phyletically retarded species, espe- 

 cially those of the American D. Lineata, and 

 perhaps also those of Zygophylli and Livornica. 

 The few observations on the development of 

 D. Galii already recorded give support to this 



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