50 Lang . — Prothalli of Ophiog loss urn pendulum 
to special points in the latter ; the various forms of L . 
Selago prothallus indicate how this may have come about. If 
this interpretation, on which the L. Phlegmaria type would 
be regarded as a highly specialized one, is correct, little 
weight can be attached to the resemblance between it and the 
prothallus of Ophioglossum ; the resemblance is further not 
a very close one. 
Important points of difference are also found when the 
sexual organs of the Ophioglossaceae and the Lycopodiaceae 
are compared. The general construction of the antheridia is 
indeed not dissimilar, but, since the plan of these organs is 
alike in all the eusporangiate Vascular Cryptogams, no weight 
can be attached to this. A point of difference is found in the 
spermatozoids, which are multiciliate in the Ophioglossaceae, 
biciliate in the Lycopodiales 1 . The archegonia in both 
groups exhibit a series from short-necked to long-necked forms. 
Their development affords a constant difference in the presence 
of a basal cell in the Ophioglossaceae and its absence in the 
Lycopodiales. The presence of a suspensor in the embryo of 
the latter group, and the origin of the primary leaf and root 
and the apex of the stem from the end furthest from the 
suspensor, are important points of difference. 
To sum up the comparison between the Ophioglossaceae 
and the Lycopodiales, it does not appear too much to say that, 
while some general resemblances standing in relation to 
similar modes of life can be traced, there are no characters, 
the morphological value of which is attested by constancy 
throughout obviously allied groups, indicating affinity between 
the two. On the other hand, important points of difference 
exist in type of symmetry, in the sexual organs, and in the 
embryogeny. 
The Ophioglossaceae are usually included in the Filicales, 
and a similar comparison must now be made with this phylum 
1 The isolated heterosporous genus Isoetes has multiciliate spermatozoids, and 
also differs from the other Lycopodiales in the absence of a suspensor. Without 
attempting to estimate the weight to be attached to these exceptions, it may 
be pointed out that their existence does not seriously affect the above comparison 
of the prothalli of the homosporous Lycopodiales and the Ophioglossaceae. 
