Pteridophytes . Are they vestigial? 243 
them in the vast majority of the leaves below the fertile zone 
may be explained on the general principle of economy, by 
which parts no longer functional are liable to obliteration 1 . 
On such grounds as these the opinion may be surely based 
that the imperfect sporangia at the base of the strobilus are 
vestigial organs , and not indicative of an upward evolution , 
leading in the race to the complete sporangium. 
Goebel, in his Organographie 2 , has pointed out that ‘ we 
must, however, guard against considering all arrested organs 
as being descended from organs which were developed in the 
ancestors of existing forms.’ He alludes to certain inflores- 
cences, and remarks that it is 4 quite a general rule that many 
more primordia of organs are formed than become functional.’ 
In this matter I think that Lycopodium in its simple way is 
instructive. We find incompletely developed sporangia, both 
at the apex and the base of the strobilus (e. g. of L. inun- 
datum) , these, however similar in appearance, seem to have 
had a different phylogenetic history.' For reasons already 
stated the basal sporangia may be held to be arrested, and 
vestigial as regards descent, and that in the ancestry they 
were represented by fully formed sporangia. But the series 
of successively smaller sporangia at the apex may be regarded 
as primordia of organs which may have never become func- 
tional in the ancestry : they are subtended by leaves of an 
arrested type, imperfect like the sporangia which they bear. 
And this is, indeed, the criterion by which such cases may be 
judged. Many apical buds, like those of Lycopodium , have 
an apparently unlimited power of forming primordia; but 
fail to mature them all : these rudiments might be described 
as phylogenetically nascent, or supernumerary ; while spor- 
angia or buds at the base of the fertile region would be 
properly regarded as phylogenetically evanescent, — as repre- 
senting parts which in the history of the race had been ac- 
customed to come to functional maturity. Thus in the case 
of Lycopodium we acquire the idea of a zone of reproduc- 
tive activity , limited below by phylogenetically evanescent or 
1 Origin of Species, chap, iv, p. 1 1 7. 2 Organography, Engl, ed., p. 60. 
