the more primitive type in the Ferns ? 1 1 7 
a doubt which is strengthened by the absence of other evi- 
dence. It is by no means an improbable view that the 
filamentous form of the Hymenophyllaceous prothallus is the 
result of adaptation to the very moist situations in which they 
commonly grow : an extreme case in fact of that lengthening 
of the germinal filament which may be produced by certain 
external conditions 1 , and that we have here to deal with 
a phenomenon of analogy with the Mosses rather than with 
an index of true affinity ; to this I shall return later. 
(iii) It will doubtless be remarked, however, that in the 
freely exposed, projecting sexual organs of the Hymeno- 
phyllaceae, and especially of Trichomanes, there is an obvious 
character which is shared with the Mosses : that is so, but the 
correspondence applies rather to the position of the organs, 
than to details of their structure. The archegonium is a typi- 
cal Fern-archegonium : it developes as a Fern-archegonium, 
and has the single neck-cell, common to Leptosporangiate 
Ferns 2 . The antheridia are borne, it is true, on a narrow 
pedicel, but their development and mature structure conform 
approximately to that in other Ferns. It is then their position 
which would provide ground for comparison rather than their 
structure ; but this protruding position is a necessary result 
of the simple structure of the prothallus, and if that be 
a result of relatively direct adaptation, as above suggested, 
so also would be the exposed position of the sexual organs. 
(iv) The presence of a single initial cell with definite seg- 
mentation at the apex of the young Moss-sporogonium, and 
also at the apex of the stem, leaf, and root of the Lepto- 
sporangiate Ferns, while such are absent or less definite in 
their segmentation in the Eusporangiate Ferns, is certainly 
a fact worthy of note. The common presence of a single 
initial in the lower forms, and the absence of it from most 
Phanerogams, may be regarded as pointing towards the con- 
clusion that those organisms which show the single initial are 
lower in the scale. Examples are however known of the 
1 See Goebel, 1 . c., p. 1 15 : also Dodel-Port, Kosmos, 1880, p. 1 1. 
3 Annals of Botany, vol. I, p. 210. 
