Volvocacew 195 



mann's genus Eudorinella 1 . Chodat 2 also considers that the two 

 described species of Pleodorina Shaw 3 should be regarded merely 

 as forms of Eudorina elegans, but the marked differentiation which 

 exists between the vegetative and reproductive cells of Pleodorina 

 does not support his view. 



Eudorina elegans Ehrenb. is widely distributed in ponds, ditches and lakes 

 all over the British Islands. The cells are 10 25 p. in diameter and the 

 colonies 40 150 p. ; fig. 77. The ellipsoid colonies of this plant are sometimes 

 described as possessing several mucous mamillate projections at one pole, but 

 I do not find this character in British examples, the colonies of which are 

 invariably globose. 



Genus Volvox (L., 1758) Ehrenb., 1830. The coenobium is 

 globose, consisting of a large number of small cells (200 22,000) 

 arranged in a single peripheral layer within the mucous investment. 

 The coenobium is a hollow r sphere and the cells are connected by 

 protoplasmic threads of varying stoutness. There is a differentia- 

 tion of the cells, the vast majority of them being purely vegetative 

 (somatic), and the remainder either parthenogonidia, androgonidia, 

 or gynogonidia. Each cell possesses a distinct chloroplast, two or 

 more contractile vacuoles, and a pair of cilia. Asexual reproduction 

 occurs by the development of new colonies from the partheno- 

 gonidia, of which about 8 (1 to 16) are found in a single coenobium. 

 These parthenogenetically formed individuals become detached in 

 the hollow cavity of the mother-coenobium and are ultimately set 

 free on its death. Sexual reproduction takes place by the fusion 

 of an antherozoid with an oosphere. The antherozoids arise by 

 the division of few or many androgonidia, which are similar in 

 appearance to the parthenogonidia. The divisions of the androgo- 

 nidia produce either a plate-like or a spherical mass of antherozoids, 

 each of which is a small fusiform body, much attenuated at the 

 anterior end and furnished with two cilia. The gynogonidia are 

 few in number, larger than the vegetative cells, and each one 

 becomes an oosphere. The oospores are globular, either smooth or 

 substellate, and their germination is direct, after a period of repose. 

 Both asexual and sexual colonies occur, and the latter, which some- 

 times possess parthenogonidia, may be either monoecious or 



1 Lemmermann in Berichte Deutsch. Botan. Gesellsch. xviii, 1900, p. 307. 



2 Chodat in Beitrage zur Kryptogamenflora der Schwciz, Bd i, Heft 3, Berlin, 

 1902, p. 152. 



3 Shaw in Botan. Gazette, 1894, xix, p. 279 ; Kofoid in Bull. Illinois State Lab. 

 v, 1898, p. 273; also in Ann. Mag. Nat. Hist. ser. 7, vol. vi, July, 1900. 



132 



