226 ORGANOGRAPHY. BOOK I. 



no doubt of the reproductive functions of the contents of what 

 is named the theca or capsule, which is a hollow urn-like body, 

 containina; sporules : it is usually elevated on a stalk, named 

 the seta, with a bulbous base, surrounded by leaves of a dif- 

 ferent form from the rest, and distinguished by the name of 

 perichcetial leaves. If this theca be examined in its youngest 

 state, it will be seen to form one of several small sessile ovate 

 bodies {pistiUidia, Agardh ; jjrosphi/ses, YAwhart ; adductores, 

 Hedwig), enveloped in a membrane tapering vip wards into a 

 point; when abortive they are called paraphyses. In process 

 of time the most central of these bodies swells, and bursts its 

 membranous covering, of which the greatest part is carried 

 upwards on its point, while the seta on which the theca is sup- 

 ported lengthens. Tliis part, so carried upwards, is named 

 the calyptra : if it is torn away equally from its base, so as to 

 hang regularly over the theca, it is said to be mitriform ; but 

 if it is ruptured on one side by the expansion of the theca, 

 which is more frequently the case, it is denominated dimidiate. 

 When the calyptra has fallen off or is removed, the theca is 

 seen to be closed by a lid terminating in a beak or rostrum : 

 this lid is the operculum, and is either deciduous or persistent. 

 If the interior of the theca be now investigated, it will be 

 found that the centre is occupied by an axis, called the co- 

 lumella ; and that the space between the columella and the 

 sides of the theca is filled with sporules. The brim of the 

 theca is furnished with an elastic external ring, or annulus, 

 and an interior apparatus, called the peristomium : this is 

 formed of two distinct membranes, one of which originates 

 in the outer coating of the theca, the other in the inner coat ; 

 hence they are named the outer and inner peristomia. The 

 nature of the peristomium is practically determined at the 

 period of the matvnity of the theca. At this time both mem- 

 branes are occasionally obliterated ; but this is an unfrequent 

 occurrence : sometimes one membi'ane only remains, either 

 divided into divisions, called teeth, w^hich are always some 

 multiple of four, varying from that number as high as eighty, 

 or stretching across the orifice of the theca, which is closed up 

 by it; this is sometimes named the tympanum. Most fre- 

 quently both membranes are present, divided into teeth, from 



