

Chap. XXVII. OF PANGENESIS. 367 



may be called metagenesis. The metagenetic process is carried 

 to an extreme degree in the development of some Echinoderms, 

 for the animal in the second stage of development is formed 

 almost like a bud within the animal of the first stage, the 

 latter being then cast off like an old vestment, yet sometimes 

 still maintaining for a short period an independent vitality. 15 



If, instead of a single individual, several were to be thus 

 developed metagenetically within a pre-existing form, the pro- 

 cess would be called one of alternate generation. The young 

 thus developed may either closely resemble the encasing parent- 

 form, as with the lame of Cecidomyia, or may differ to an 

 astonishing degree, as with many parasitic worms and with 

 jelly-fishes ; but this does not make any essential difference in 

 the process, any more than the greatness or abruptness of the 

 change in the metamorphoses of insects. 



The whole question of development is of great importance 

 for our present subject. When an organ, the eye for instance, 

 is metagenetically formed in a part of the body where during 

 the previous stage of development no eye existed, we must look 

 at it as a new and independent growth. The absolute independ- 

 ence of new and old structures, which correspond in structure 

 and function, is still more obvious when several individuals are 

 formed within a previous encasing form, as in the cases of 

 alternate, generation. The same important principle probably 

 comes largely into play even in the case of continuous growth, 

 as we shall see when we consider the inheritance of modifica- 

 tions at corresponding ages. 



We are led to the same conclusion, namely, the independ- 

 ence of parts successively developed, by another and quite 

 distinct group of facts. It is well known that many animals 

 belonging to the same class, and therefore not differing widelv 

 from each other pass through an extremely different course of 



EST I C fT ^^ n0t in ^ ^ remarkably 

 different rom others of the same order, undergo what has been 



caned a hyper-metamorphosis-that is, they pass through an 

 ear y stage wholly afferent from the ordinary grub-like larva. 

 In the same sub-order of crabs, namely, the Ma_, as Fritz 



- Prof. J. Eeay Greene, in GuntherV Record of Zoolog. Lit.,' 1865, p. 625. 



