264 | MR. J. R. VAIZEY ON THE ANATOMY AND 
ll. COMPARATIVE ACCOUNT OF THE MORPHOLOGY OF THE 
SPOROGONIUM OF THE Musor. 
The Polytrichacee which, for the reasons mentioned above, 
were selected for special and detailed examination, were found to 
differ very greatly from all the other Musei in certain points of 
their structure; so much so that they seem to form a group by 
themselves. Hence, as far as possible, wherever the structure 
of the Polytricha under consideration differs materially from 
the other Musci, reference is made to species from other Orders, 
so that a more general view of the whole group may be 
obtained. 
1. External Morphology. 
The sporogonium of the Musci may be divided into three parts, 
namely, the foot, the sefa, and the theca. 
The term foot is applicable properly only to that portion which 
can be shown to be developed from the hypobasal cell; but for 
convenience, and as it has not yet been shown accurately how 
inuch is developed from the hypobasal cell, I shall call that part 
of the sporogonium the foot which is placed within the vaginula. 
The seta is the portion of the sporogonium between the foot 
and the theca. 
The term theca is applied to the apophysis together with the 
sporangium and its operculum &c. The theca is thus divided 
into two members. 
The mature sporogonium has the tip of the foot turned up- 
wards, as may be seen when it is pulled out of its sheath, or, better 
still, by means of a longitudinal section (Pl. IX. fig. 2, Pl. X. 
fig. 15). The angle where the true morphological apex is turned 
up will frequently be referred to as the apex of the foot, although 
it is evidently not the true morphologic apex. The epidermal 
cells of the seta are not paralle) to the axis of the seta, but are, 
as in the stems of many vascular plants, spirally twisted. 
In external morphology there is a considerable difference 
between the theca of the Polytrichacesm, in those forms in which 
the apophysis is developed, and that of other Musci; in all those 
forms in which the apophysis is absent, the thec® are similar. 
Among the Polytrichaces, the apophysis is absent in the genera 
Atrichum (Catharinea), Oligotrichum, and many Pogonata. In 
other Orders of the Musci, e. g. Splachnacem, Funariace», 
