1896. 



THE MEANING OF METAMORPHOSIS. 



397 



there is any distinct old age, and in very primitive forms also the 

 marks of decline in the ontogeny may not exist, or may be difficult of 

 observation, e.g., Orthoceratidae and the like. 



Table of Ontogenic Terms. 



Structural 

 Conditions. 



Anaplasis 

 (Haeckel) 



Metaplasis 

 (Haeckel) 



Stages. 

 I Embryonic 



Larval or 

 young 



Immature or 

 adolescent 



Mature or 

 adult 



Stages. 

 Embryonic 



Nepionic 



Neanic 



Ephebic 



Paraplasis Senile or old Gerontic 



Sub-stages. 

 Several 



ananepionic 



metanepionic 



paranepionic 



ananeanic 



metaneanic 



paraneanic 



anephebic 



metephebic 



parephebic 



anagerontic 



metagerontic 



paragerontic 



Sub-stages. 

 No popular 



It will, of course, be understood that the artificial sub-division of 

 each stage into three sub-stages is merely a matter of convenience. 

 In our own experience, we sometimes find only two, and sometimes 

 more than three, sub-stages, but in a large number of cases all the 

 changes within any one stage may be described under three headings. 

 It does not appear that the epembryonic (postembryonic) changes 

 taking place in the earlier life-histories of the first nine orders of 

 Insecta, and classifiable under the term of direct development, 

 can in any way be separated from those of other animals. The wings 

 are not introduced suddenly in the Orthoptera, for example, nor, for 

 that matter, in any other orders. Their development is strictly a 

 phenomenon accompanying the nepionic or neanic stages of insect 

 development, and the last stage in the orders from x. to xvi. is the 

 pupal stage. The unfolding of the wings, of course, takes place in 

 the ephebic stage, but this is not a change in which new structures 

 appear. Their expansion and hardening is a mechanical result of 

 unfolding and use taking place in structures elaborated in the pupa] 

 stage and probably inherited from animals in which such structures 

 arose more gradually and became hardened and shaped by usage in 

 more prolonged substages of growth. 1 



1 Mr. Alfred G. Mayer, who has been working up this and connected subjects 

 among Lepidoptera, and whose researches are original and thorough, and accom- 

 panied by drawings that will, when published, demonstrate his discoveries, has, at 

 our request, furnished us with the following note in support of the conclusion 

 stated above, that the changes taking place in the development of the wings are not 

 so sudden and startling as they appear to be : — 



" In the Lepidoptera the rudiments of the wings have been found in very young 

 larvae, Landois having demonstrated them in larvae only 4 mm. long. My own 

 researches have shown that they occur in the second and third thoracic segments, 

 and consist merely of thickened infolded portions of the hypodermis itself. The 

 cells of the larval wings are very much crowded together, and are elongate spindle- 

 shaped. When the larva changes into a pupa the wings expand to about sixty times 



