3«4 



MUSCINE2E. 



form a membrane ; in this case the teeth appear split from one another above, and the 

 endostome (the inner peristome) is composed of a lattice-work of longitudinal or trans- 

 verse ridges instead of cilia (Fig. 267). A great variety is met with here, which may 



Fig. 2ji.—Ft(naritt hygrometrtca ; part of a longitudinal 

 section of an unripe theca. 



Pig. ■2T2,—Fiaiaria hygrotnetrica ; part of a transverse section 

 through the operculum. 



Fig. 273.-^4 longitudinal section of the theca oi Poly- 

 trichtim J>ili/erum. (after Lantzius-Beninga, X is) ; B the 

 transverse section (X about 5) ; w wall of the theca, cu 

 operculum, c c columella, / peristome, ep epiphragm, a a 

 annulus, i i the air-cavities penetrated by alga-like cel- 

 lular filaments, s spore-sac, containing the primary mother- 

 cells of the spores, st the seta, the upper part of which 

 forms the apophysis ap. 



easily be understood by the beginner when he has obtained a clear idea of the principle. 

 The inner and outer sides of the teeth of the peristome are hygroscopic to a different 



