Notes. 
1 68 
neighbours. But such a growth of Mosses and Hepaticae is of such 
general occurrence that, if the filamentous condition be an adaptation 
for this special end, one can only speculate why it has not arisen 
in a host of other Fern-prothallia to which it would be equally 
useful. 
Again, in Trichomanes, although the prothallium is generally fila- 
mentous, yet small cellular bodies or even flat expansions, which 
remind us of other Fern-prothallia, are formed to carry the archegonia. 
Goebel explains this as due to the need of a better supply of nutriment 
for the archegonium. On the other hand the existence of such 
cellular bodies might be quoted as evidence of reduction from the 
more usual form of prothallium. But if the retention of cellular 
masses for the nutrition of the archegonia was needful in the case of 
Trichomanes , why, we may ask, is a similar feature absent from the 
prothallium of Schizaea ? It is difficult to imagine that the absence of 
the meristematic archegoniophore is an adaptive feature. 
It would seem, therefore, that Goebel’s explanation is , the correct 
one, and that the condition of things in Schizaea is a primitive condi- 
tion, even more so than that existing in Trichomanes. 
The whole vegetative structure of the prothallium of Schizaea is 
eminently suggestive of one of the filamentous Algae. That the 
Ferns as well as other higher plants have descended from an aquatic 
ancestor is of course rendered probable by the character of the ciliate 
spermatozoids. But a specially interesting feature in Schizaea is the 
mode of development of both kinds of sexual organs as morpho- 
logical equivalents of the ordinary branches of a filamentous pro- 
thallium, a mode which explains the character of these, organs. Are 
we not therefore justified in regarding Schizaea as a primitive form ? 
The question, however, is not one which can be decided by the 
evidence derived from a single form, but must rest on a broad basis 
of comparison of the development in the different families of Ferns. 
Nevertheless the probability of the filamentous prothallium being 
primitive is increased by its occurrence in the separate families of 
Hymenophyllaceae and Schizaeaceae. When we add to this the 
frequency of a filamentous stage at the beginning of the development 
of so many different types of Ferns, and the tendency to form fila- 
mentous prothallia when nutrition is inadequate, we have accumulated 
a weighty body of evidence in favour of the hypothesis. 
It may be observed that the characters of the Schizaeaceae show 
