6 TRANSFORMATIONS OF INSECTS. 



to sharks and whales, and to turn into something much more 

 dissimilar than butterflies are to caterpillars — into barnacles. 

 Instead of their development progressing during the metamor- 

 phosis it retrogrades, and the adult creature is less perfect 

 than the young. 



Swammerdam, the great Dutch naturalist of the 17th century, 

 laboured to prove that the structural elements of the perfect insect 

 were already within the caterpillar or larva, and he impressed upon 

 his contemporaries and upon many of his successors that all the 

 parts of the adult were in the creature as it escaped from the egg, 

 but on a small scale. He considered that the glories of the fully- 

 developed insect were masked in the tiny grub, and hence the 

 name of larva. But careful anatomical researches and dissections, 

 with the aid of the microscope, gradually disproved this idea of 

 Swammerdam's, and by the beginning of this century the 

 opinions of naturalists concerning the nature of the metamor- 

 phoses of the Artiadata were much nearer the truth. 



It had become known that some important organs which 

 existed at one period of insect life were not to be found at others, 

 and that new combinations of structures having peculiar functions 

 and uses appeared during growth. 



Every one knows that a young chicken differs in shape from 

 one just hatched. Now, the anatomists of the early part of this 

 century laboured at the investigation of the alterations in the 

 arrangement of the internal parts and organs which took place 

 during the &<g^ life of the bird, and they proved that the develop- 

 ment within the &g^ was akin to that which entomologists were 

 obtaining dim notions about with respect to the metamorphoses 

 of insects. Later still, Von Baer and Rathke asserted that the 

 early condition within the ft^^ — the embryo — of all animals, had 

 one aspect, but that soon essential differences in structure com- 

 menced, and determined the future shape and peculiarities of the 

 adults. This is not consistent with modern research, nor is it 

 true that the most important organs appear first of all in the 

 earliest stages of life; but these theories had excellent effects 

 upon the progress of science. And Milne-Edwards proved that 

 the embryos of the kinds of Crustacea, which, when fully grown, 

 are of the same genera or groups of species, resembled each 



