the more primitive type in the Ferns ? 1 1 5 
a branched filament, there may have been also a degeneration 
of the sexual generation, as seems to me probable in the case 
of the Fern-prothalli even at the present day/ It is further 
added in a note that ‘the degeneration is in many cases 
brought about by the transfer of the formation of sexual 
organs to earlier periods of development of the prothallus.’ 
That there is a similarity between the protonema of the 
Moss and the prothallus of the Hymenophyllaceae no one 
can doubt ; but before it could be finally accepted that the 
filamentous form is in both families really a primitive charac- 
ter, and not a result of more direct adaptation to similar 
external circumstances, which took place independently in the 
two families, we should require more evidence as to the details 
of descent than is as yet forthcoming, and the conclusion will 
need to harmonise with other facts relating to form and de- 
velopment of these and other organisms. I am not prepared 
at present to concede this point without considering carefully 
the grounds on which the opinion is founded. To this end we 
may first take up the question whether the filamentous form 
was the original one for the sexual generation of the Bryo- 
phyta : and secondly, we may inquire whether the similarity 
of form between the protonema of the Mosses and the fila- 
mentous prothallus of the Filmy Ferns is an indication of real 
affinity. 
Having shown that among the Mosses there are forms in 
which the leafy plant is of very small size, and simple struc- 
ture as compared with most Mosses, so that the protonema 
constitutes the greater part of the sexual generation, Goebel 
states that ‘ the appearance of a protonema on the germination 
of spores of the Mosses cannot be regarded as a “ phenomenon 
of adaptation,” but as a peculiarity inherited from their an- 
cestors V This conclusion follows from the recapitulation- 
theory 2 , which, however, is a much less safe guide in the 
embryology of plants than in that of animals. I have else- 
where expressed at length my doubts of the propriety of 
basing broad phylogenetic conclusions upon details of external 
1 1 . c., p. 1 1 2. 2 Goebel, Muscineen: Schenks Handbuch, II, p. 387. 
