522 Bower.—Studies in the Phytogeny of the Filicales. 
wedge-shaped cell from which segments have been cut off right and left, 
is seen on edge ; in ^ it is seen from the side, and the segments themselves 
have divided into equal halves, thus giving the four-rowed structure of the 
stalk, as seen in e when cut transversely. In c, d, which show views from 
above, the two-sided segmentation is clearly demonstrated ; while in g 
the cap-cell has been cut off, and has already divided. Thus the segmenta¬ 
tion of the sporangium in Metaxya accords with that of Cheiropleuria and 
Dipieris. It has been shown that Metaxya on comparative grounds may 
be held as related to Lophosoria , and be regarded as a Gleichenioid deriva¬ 
tive. Dipteris and Cheiropleuria have probably a similar relation, and all 
the three genera correspond in this uncommon feature of the two-rowed 
segmentation of the sporangial primordium. 
Lastly, for purposes of comparison, a section of the fertile region of the 
leaf of Platycerium is represented in PI. XXV, Fig. 1 6. Here the leaf is 
thicker than in Cheiropleuria , and the sori are localized above the recepta- 
cular strands. It is clear from the section that the latter run here in a plane 
much nearer to the lower surface than the strands of the regular venation. 
In Cheiropleuria (Text-fig. 15) the difference of level between the recepta- 
cular strand and the true venation is only slight; but here, in Fig. 16, 
strands of the two systems are seen directly superposed, and several layers 
of cells intervene between them. This is in accordance with what has 
been stated above (p. 512), and with the drawing of Mettenius (Filices, 
Hort. Lips., PI. 4, Figs. 1-3). It may also be noted that the three 
sporangia shown in Fig. 16 are at approximately the same stage of 
development, though that which is median is slightly in advance of the 
others. This is characteristic for Platycerium . The origin of the sporangia 
is almost simultaneous, but slight differences of time may be observed in 
them. 
Comparisons and Conclusions. 
It will be evident from this detailed description of Cheiropleuria , 
incomplete as it is, and entirely deficient as regards the gametophyte, that 
the genus is one which has a special comparative interest ; and that 
the interest lies, not only in the location of the Fern in its own probable 
phyletic position, but also in the demonstration that it brings of the 
divergences from strict parallelism, in respect of the various characters 
which are used as criteria in such comparisons. It is only when such 
divergences are fully taken into account that a correct valuation can be set 
upon the method of phyletic study, based upon such comparisons, and of 
the conclusions which follow from them. 
The first question will be as to the probable phyletic position of 
Cheiropleuria , and especially its connexions downwards in the scale. Then 
may follow the question of its probable relations upwards , with forms still 
