240 DESCEIPTION OF \^Polygastrica» 



being formed between the ongiual segments, which in otlier respects 

 remain unaltered. 



DiDTMOPEnm Grevillii.^IIyalot'heca eylindrica. (Ehr.) — Sheath dis- 

 tinct; joints of the filament broader than long, with a thickened 

 border at their junction ; transverse view broadly elliptic. The sheath 

 is jointed as well as the filaments. 



In conjugating, it separates into single joints : the joints or cells 

 become connected by a narrow process, often remarkable for its 

 length, and the contents of one cell pass through it into the other, 

 and a sporangium is formed in the same maimer as in many of the 

 Conjugate. 



The transfer of the endochrome takes place in a mass. After the 

 completion of the process, the empty cell is frequently detached, as 

 also occurs in those Conjugates which bear the sporangiimi within 

 the cell. 



In a front view, the sporangium is as orbicular as the quadrate 

 form of the joint will permit. The mucous covering remains im- 

 altered on the joints when they are coupled. 



D. Borreri. — Joints inflated, ban'el-shaped, longer than broad ; 

 transverse view cfrcular. Filaments pale green, very slender, their 

 mucous sheath wanting or indistinct ; angles of joints bi-crenate. 

 On account of the length of the joints, the disposition of the endo- 

 chrome in two portions is very distinct. The joints have not a 

 thickened border as in B. GreveUii, and the filament separates with 

 less facility into single joints. (P. 13, f. 38, 39 ; fig. 38 a transverse 

 view). The sporangium is elliptic and lies between the cells which 

 remain attached to it. 



Kiitzing suggests that this plant may be identical with the Gym- 

 nozyga moniliformis, of Ehi'enberg. 



Genus DESMXDniM. — Filament fragile, elongated, triangular or 

 quadrangular, regularly t\\isted ; joints bidentate at the angles. This 

 organism is of a pale green colour and slightly opaque ; when dried, 

 the British species usually acquire a yellowish appearance, and adhere 

 to paper or talc less firmly than plants belonging to allied genera. The 

 filaments are regularly twisted, but being triangular or quadrangular, 

 two of the bidentate angles of each joint are always visible at the 



