Chap. XIV.] DEVELOPMENT AND EMBRYOLOGY. 239 



would have retained through inheritance, if they had 

 really been metamorphosed from true though extremely 

 simple legs, is in part explained. 



Development and Embryology. 



This is one of the most important subjects in the 

 whole round of natural history. The metamorphoses of 

 insects, with which every one is familiar, are generally 

 effected abruptly by a few stages ; but the transforma- 

 tions are in reality numerous and gradual, though 

 concealed. A certain ephemerous insect (Chloeon) 

 during its development, moults, as shown by Sir J. 

 Lubbock, above twenty times, and each time undergoes 

 a certain amount of change ; and in this case we see 

 the act of metamorphosis performed in a primary and 

 gradual manner. Many insects, and especially certain 

 crustaceans, show us what wonderful changes of 

 structure can be effected during development. Such 

 changes, however, reach their acme in the so-called 

 alternate generations of some of the lower animals. It 

 is, for instance, an astonishing fact that a delicate 

 branching coralline, studded with polypi and attached 

 to a submarine rock, should produce, first by budding 

 and then by transverse division, a host of huge floating 

 jelly-fishes ; and that these should produce eggs, from 

 which are hatched swimming animalcules, which attach 

 themselves to rocks and become developed into branch- 

 ing corallines; and so on in an endless cycle. The 

 belief in the essential identity of the process of 

 alternate generation and of ordinary metamorphosis 

 has been greatly strengthened by Wagner's discovery 

 of the larva or maggot of a fly, namely the Cecidomyia, 

 producing asexually other larvae, and these others, which 



