266 GENERATION AND DEVELOPMENT OF DESMTDIACEiE. 



green and granular contents ; by degrees the envelope acquires in- 

 creased thickness, and the contents of the spore-cell become brown 



or red. The surface of the 

 Fig. 113. Sporangium, as this body 



is now termed, is some- 

 times smooth, as in Clos- 

 terium and its allies (Fig. 

 114) ; but in the Cosma- 

 riece, it acquires a granu- 

 lar, tuberculated, or even 

 spinous surface (Fig. 113), 

 the spines being some- 

 times simple and some- 

 times forked at their ex- 

 tremities.* — The mode in 

 which conjugation takes 

 place in the filamentous 

 species constituting the 

 Desmidiece proper, is, how- 

 ever, in many respects 

 different. The filaments 

 first separate into their 

 component joints ; and 

 when two cells approach in 

 conjugation, the outer cell- 

 Conjugation of Cosmarium botrytis.—x, wall of each splits or gapes 

 mature frond ; b, empty frond ; c, transverse at that part which adjoins 

 view ; d, sporangium with empty fronds. the other cell, and a new 



growth takes-place, which 

 forms a sort of connecting tube that unites the cavities of the two 

 cells (Fig. 115, d, e). Through this tube the entire endochrome 

 of one cell passes-over into the cavity of the other (d), and the 

 two are commingled so as to form a single mass (e), as is the case 

 in many of the Conjugates (§ 251). The joint which contains 

 the Sporangium can scarcely be distinguished at first (after the 

 separation of the empty cell), save by the greater density of its 

 contents ; but the proper coats of the sporangium gradually become 

 more distinct, and the enveloping cell-wall disappears. — The subse- 

 quent history of the Sporangia has hitherto been made out in only 

 a few cases. From the observations of Mrs. H. Thomas (loc. cit.) 

 on Cosmarium, it appeared that each sporangium gives origin, not 

 to a single cell but to a brood of cells ; and this view is fully con- 

 firmed byHoffmeister ("Ann. of Nat. Hist.," 3rd Ser., Vol. i. 

 1858, p. 2), who speaks of it as beyond doubt that the contents of 



* Bodies precisely resembling these, and almost certainly to be regarded 

 as of like kind, are often found fossilized in Flints, and have been 

 described by Ehrenberg as the remains of Animalcules, under the name 

 of Xanthidia. 



