278 THALLOPHVTES. 



secondary conidia, and of projecting them to some distance. If one of these happens 

 to strike a fly upon the white area of the under surface of its body, it sends a hypha 

 through the skin, and there forms toruloid cells, which multiply by germination and 

 are disseminated in the blood throughout the body of the fly. These finally grow into 

 hyphae which penetrate the skin, each forming a conidium, which is cast off with con- 

 siderable force. 



C— VOLVOCINEiE *. 



[This group includes two genera, Vol'vox and Eudorina, which resemble Pandorina in 

 many respects, and were formerly included with it in one group. Like Pandorina^ these 

 plants are motile, and consist of a number of ciliated cells aggregated into a coenobium. 

 In Eudorina, which so much resembles Pandorina as to be sometimes mistaken for it, the 

 number of cells is 16 or 32; in Vol'vox it is very great, amounting even to thousands. 

 The cells are so arranged as to form the wall of a hollow sphere. The distinction 

 between these plants and Pandorina is that in them certain cells of the coenobium 

 develope into antheridia and oogonia. In Eudorina four of the cells become antheridia, 

 and the remainder oogonia : in Vol'vox a certain number only of the cells take on the 

 function of reproductive organs. The antherozoids formed in the antheridia escape and 

 make their way through the wall of an oogonium to the oosphere which it contains, and 

 fertilise it. The oosphere then surrounds itself with a firm double cell-wall, and 

 assumes a red colour: it becomes an oospore. 



Non-sexual reproduction is effected by the repeated division in Vol'vox of certain 

 cells (gonidia) of the coenobium, and in Eudorina of all the cells. In the former, the 

 young coenobia which are thus formed escape into the cavity of the mother-coenobium, 

 where they remain until they are set free by its death and disintegration : in the latter, 

 they are at once set free. 



Sexual and non-sexual reproduction do not go on simultaneously in the same 

 coenobium of Fblvox, and in one species (Vol'vox minor, Stein) the male and female 

 organs are not produced in the same coenobium, whereas this is the case in Vol'vox 

 Globator, L. 



The germination of the oospore has been observed by Kirchner in Vol'vox minor. The 

 protoplasmic contents divide into two, and this is repeated until about 500 small cells 

 have been produced ; these are arranged like those of the adult coenobium. The wall of 

 the oospore gradually deUquesces, and the young coenobium is set free.] 



D. — CEdogonie^e. 



The CEdogoniesB ^ include at present only the two genera (Edogonium and Bulbo- 

 crcete, the few species of which are common in fresh water, fixed by an organ of attach- 

 ment at the lower end to solid bodies, mostly the submerged parts of other plants. 

 The thallus consists of unbranched {(Edogonium) or branched {Bulbochsete) rows of 

 cells, which multiply by intercalary growth, while the terminal cells elongate into hyaline 

 bristles. The longitudinal growth of the cylindrical cells begins with the formation of 

 an annular cushion of cellulose inside the cell, close beneath its upper septum ; the 

 cell-wall ruptures at this place circularly; the ring of cellulose then stretches, and a 

 broad transverse zone is thus intercalated in the wall of the cell. The process is 

 constantly repeated immediately beneath the older very short upper piece of the cell, 



^ [On Volvox, see Cohn, Beitr. z. Biol. d. Pflzn. I. 3, and Kirchner, ibid. II. i : on Eudorina see 

 Carter, Ann. of Nat. Hist., ser. III. vols. 2 and 3.] 



^ Pringsheim, Morphologie der Qidogonieen, Jahrb. fiir wissen. Bot. vol. I. De Bary, Ueb. 

 (Edogonium u. Bulbochcete, 1854. — Juranyi, Jahrb. d. wiss. Bot. IX. [Ann. des Sci. Nat. 1856, 

 vol. V. p. 251.— Carter, Ann. and Mag. Nat. Hist. 1858, vol. I. pp. 29-39.] 



