THE PALEONTOLOGIC RECORD 297 



no necessary relation to the onto-stages, even if tliey coincide with them. 

 We have thus a second group of stages, which we may designate form 

 stages, or morphic stages, and there will be required distinct designa- 

 tions in each case. The best method of naming these stages is to refer 

 them to the adult ancestral type which they represent. 



Thus, in all species of the gastropod shell Fusus, the earliest morphic 

 stages are a close recapitulation of the adult of Fusus porrectus of the 

 Eocenic. These stages may therefore be called the F. porrectus stage. 

 It may be continued for a considerable period of the early life history, 

 covering several onto-stages, or it may be condensed into a short por- 

 tion of one stage or substage, in accelerated individuals. 



It is of considerable importance that onto-stages and morphic stages 

 should be discriminated, so I will introduce another illustration. 



In the Miocenic of the Atlantic coast we have the gastropod genus 

 Fulgur well represented. Fulgur fusiformis is normally characterized, 

 in the adult, by the possession of a pronounced flat shoulder, which is 

 separated from the body of the shell by an angulation carrying rounded 

 tubercles. Some of the more specialized individuals lose the angula- 

 tion and tubercles in the last whorl and become rounded. Thus, while 

 normally the species is tuberculated in the ephebic onto-stages, special- 

 ized individuals acquire a new morphic stage through the loss of orna- 

 mentation. This morphic stage is prophetic of the normal adult of 

 Fulgur maximum, and hence may be called the F. maximum stage. 

 F. maximum itself has in its nepionic onto-stage the characters of 

 adult F. fusiformis; hence it may be designated the F. fusiformis stage. 

 Some individuals acquire a new stage, namely, a spinous stage, char- 

 acteristic of the adult of F. carica. In the type designated as F. 

 tritonis, the nepionic stage is characterized by a fusiformis morphic 

 stage, the neanic largely by the maximum stage, though some of the 

 later neanic stages may actually acquire the carica stage. In less 

 specialized individuals the maximum stage may continue into the early 

 ephebic in more specialized ones it ceases early in the neanic, the carica 

 stage taking its place. Finally, Fulgur carica is characterized by the 

 elimination of the maximum morphic stage, so that the neanic as well 

 as the ephebic onto-stages are characterized by the spines of the carica 

 stage, which may even begin in the late nepionic. 



In the foregoing, the different morphic stages are shown to be 

 telescoped with the onto-stages, appearing either earlier and earlier in 

 the ontogeny of successive individuals, through the operation of the 

 law of acceleration or tachygenesis ; or later and later, through the 

 operation of the complementary law of retardation or bradygenesis. 

 These laws are, of course, only applicable to an orthogenetic series, but 

 in such a series they are competent to produce, by interaction, all 

 conceivable combinations of characters. 



