248 INSECT TRANSFORMATION 



Now when we compare the various life-histories and differing 

 larval types thus briefly surveyed, a few general principles 

 seem to be apparent. Low-grade animals undergo more 

 profound changes after hatching than high-grade creatures 

 do, jellyfishes and starfishes starting free life, for example, 

 in a condition comparable to the early embryos of vertebrates 

 and arthropods ; and within the vertebrate phylum, the 

 lowly, cold-blooded amphibians undergo a transformation 

 unknown among the highly-organized, warm-blooded birds 

 and mammals. The change from marine to terrestrial life 

 appears to be accompanied by the elimination of larval stages 

 from the life-history, as is seen when we compare the newly- 

 hatched whelk with the baby snail, or the trochophore of a 

 sea-annelid with the elongate, well-segmented young earth- 

 worm just out of its cocoon. And it may be remarked here 

 that the change from marine to freshwater surroundings also 

 often seems to bring about a suppression or modification of 

 delicate larval forms ; the newly-hatched oyster is a ciliated 

 " veliger " larva, while the infant pond-mussel is a " glochi- 

 dium ' already provided with a simple bivalve shell and 

 adapted for attaching itself to some fish on which it may live 

 as a temporary parasite. Animals which produce large fully- 

 yolked eggs rarely undergo marked transformations after 

 hatching, as has been seen in the examples given of cuttle- 

 fishes and birds, and as may also be noted in the reptiles 

 (lizards, snakes, tortoises and crocodiles), which though cold- 

 blooded as the frog is, produce large eggs like those of birds, 

 which are indeed so closely akin to them as to have been 

 described by a master in vertebrate anatomy as " transformed 

 and glorified reptiles ". The eggs of the non-transforming 

 mammalia are indeed small, but these creatures provide 

 otherwise by means of the mother's blood for the rich 

 nourishment of their young before birth. 



The transformations of insects seem to offer in many 

 respects startling exceptions to the general rules thus deduced 

 from a comparative study of transformation in other groups 

 of animals. Many insects undergo very striking changes in 

 the course of their growth ; yet insects are pre-eminently 

 dwellers on the land and in the air, they produce relatively 

 large eggs with much yolk, and they are the most highly- 



