209 
Lang. — On the Sporogonium of Notothylas. 
ance of the archesporial layer derived from the amphithecium, even when 
the central cells are fertile, suggests an origin from forms with a sterile 
columella. In other words, the fertility of the endothecium in some 
cases seems better explained as the resumption of a lost power than as 
a persisting primitive feature. An origin from forms with a larger capsule 
seems also to be indicated by the preparations for splitting of the wall of 
the capsule into two valves extending to the base, even though the sporo- 
gonium is usually almost enclosed by the calyptra and effective dehiscence 
rendered impossible. I incline to look upon Notothylas as a rather arti- 
ficial genus, including a number of forms derived by reduction in size of 
sporogonia from one or more Anthoceros - like forms. Accompanying the 
reduction are the changes in development of the regions of the embryo ; 
these, though becoming manifest in reduced forms, may have an important 
bearing on the morphology of the Anthocerotaceous type of sporogonium. 
The possibility or probability that the ancestral forms of the Antho- 
cerotales had, like the other Hepaticae, a central sporogenous tissue derived 
from the endothecium does not lead us far in the search for the ancestry 
of this very natural and isolated group. In considering this question, all 
the peculiarities of cell structure, of the gametophyte and sexual organs, 
and of the sporogonium must be taken into account. There appears to be 
no indication at present of any natural relationship being established 
between the Anthocerotales and any particular series of Hepaticae. 
Whether they were derived from primitive forms of the same stock as the 
other Hepaticae, or independently, but by corresponding steps from what 
we provisionally assume as the unknown Algal ancestral forms, or whether 
on the other hand reduction has played a part in the origin of the group as 
we now have them, seem to be at present open questions. 
EXPLANATION OF FIGURES IN PLATE XXI. 
Illustrating Dr. Lang’s Paper on the Sporogonium of Notothylas . 
Fig. i. Outline of a branch system of the thallus of Notothylas Breutelii bearing sporogonia of 
various ages, x 5. 
Fig. 2. Calyptra enclosing an almost mature sporogonium, the tip of which projects : the 
ridges on the calyptra are indicated, x 16. 
Fig. 3. A dwarf sporogonium drawn to the same scale as the one in the preceding figure. 
Fig. 4. Median longitudinal section of a similar sporogonium to that in Fig. 2, showing its 
relation to the thallus, the regions of the sporogonium, the gradual ripening of the spores from above 
downwards, and the absence of a sterile columella except at the extreme base, x 20. 
Fig. 5. Longitudinal section of a similar but slightly less advanced sporogonium, which is 
completely enclosed within the calyptra. x 45. 
Fig. 6. Small portion of a median longitudinal section of a mature capsule, showing the 
arrangement of elaters and spores and the absence of a sterile columella, x no. 
