Page:Popular Science Monthly Volume 77.djvu/303

Rh no necessary relation to the onto-stages, even if they 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 designations 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 portion 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 angulation and tubercles in the last whorl and become rounded. Thus, while normally the species is tuberculated in the ephebic onto-stages, specialized individuals acquire a new morphic stage through the loss of ornamentation. 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, characteristic 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.