240 Lady Isabel Browne. 
aquatic ancestor is, of course, rendered probable by the character 
of the ciliate spermatozoids. But a specially interesting feature in 
Schizcea is the mode of development of both kinds of sexual organs 
as morphological equivalents of the ordinary branches of a fila¬ 
mentous prothallium, a mode which explains the character of these 
organs. Are we not, therefore, justified in regarding Schizcea as a 
primitive form ? ” (36). If by morphological equivalents are to be 
understood homologous members, the above quotation would mean 
that the archegonia and antheridia of Schizcea were once, in their 
phylogeny, branches. Otherwise the words are merely a fanciful 
description in scientific language. But if archegonia are homologous 
with any more primitive structure, it is with oogonia, organs found 
in various positions. Even if we accept the primitiveness of 
Schizcea among vascular plants, it is presumably less primitive than 
the cellular Cryptogams from which it would then have arisen; but 
in many of these well-differentiated gametangia occur. Surely it 
is time to recognize that the gametangium is probably an organ sui 
generis and not a transformation of another organ, or at least to 
admit that a peculiar mode of development of the gametangia in a 
recent fern is not a proof of such extreme primitiveness as claimed 
by Mr. Thomas and that the homology of the gametangium is not 
to be decided by its mode of development in a relatively highly 
differentiated and vascular plant. It is only fair to add that Mr. 
Thomas states that the question cannot be decided on evidence 
from a single form, “ but must rest on a broad basis of comparison 
of the development in the different families of Ferns” (38). He 
contends, however, that the occurrence of a filamentous prothallus 
in the Hymenophyllacese and Schizaeacese and the frequency of a 
filamentous form in the earlier stages of development, and the 
tendency to become filamentous when nutrition is inadequate 
favour the view of the relative primitiveness of the filamentous 
prothallus. But if being widely spread is a sign of primitiveness 
the thalloid prothallus would be the primitive one, for it is far 
more widely spread among the Ferns. The tendency to become 
filamentous when nutrition is inadequate is surely a weighty 
argument in favour of this condition being due to reduction. The 
frequent occurrence of a filamentous stage in the early phases of 
development certainly favours the primitiveness of this condition, 
but it can hardly be held to weigh against so many and such strong 
indications that the filamentous type is reduced. 
We may now compare the Schizseaceae with the Botryopteridea;. 
