AND THE LOWER ANIMALS. 117 



when obliged to confess that lie could not see the 

 characteristic organs of the butterfly in less-advanced 

 caterpillars, attributed their apparent absence to the 

 feebleness of his powers of vision, and the imperfect 

 state of his instruments. Thanks to the means of 

 investigation we possess nowadays, we can assert 

 most positively that the young caterpillar has neither 

 wings, nor antennas, nor even a proboscis. But at all 

 events we have been shown by our predecessors' ob- 

 servations that none of these organs appear suddenly, 

 that the most abrupt changes have been in progress 

 for a long while, and that in insects, as in all other 

 animals which undergo metamorphoses, their pheno- 

 mena are gradual and progressive. There is this 

 distinction, however : that which in Mollusks, Worms, 

 Crustacea, and Batrachia takes place openly, is con- 

 cealed in insects by a veil, which is only removed 

 when everything has been completed. Moreover, in 

 this latter class, the Hemiptera and Orthoptera manifest 

 the same continuity in their metamorphoses which we 

 observed in other instances. 



The phenomena associated with the inmost nature 

 of living beings are too far beyond the grasp of 

 human knowledge to admit of our framing even an 

 hypothesis as to the primary cause of metamorphoses ; 

 but, without outstepping the limits of a fair reserve, 

 we can at least in certain cases conjecture what is 

 the immediate cause. 



In the earlier pages of this work we contrasted the 

 voluminous vitellus of ovipara with the very small one 

 of vivipara ; and we saw how the former was sufficient 

 for the formation and afterwards for the growth of the 

 embryo, whilst the latter could only discharge one of 



