MICROSCOPIC FORMS OF VEGETABLE LIFE. 24:3 



jugation' under another form) is a reproductive globule or oo-spore; 

 which speedily becomes enveloped by an internal smooth membrane, and 

 with a thicker external coat which is usually beset with conical-pointed 

 processes (fig. 4); and the contained chlorophyll gives place, as in Pal- 

 moglwa ( 229), to starch and a red or orange- colored oil. As many as 

 forty of such ' oo-spores ' have been seen by Dr. Cohn in a single sphere 

 of Volvox, which thus acquires the peculiar appearance that has been dis- 

 tinguished by Ehrenberg by a different specific name, Volvox stellatus. 

 Soon after the ' oo-spores ' reach maturity, the parent-sphere breaks up, 

 and the oo-spores fall to the bottom, where they remain during the win- 

 ter. Their further history has since been traced out by Kirchner; who 

 found that their germination commenced in February with the liberation 

 of the spherical ' endospore' from its envelope, and with its division into 

 four cells by the formation of two partitions at right angles to one an- 

 other. These partially separate, holding together only at one end, which 

 becomes one pole of the globular cluster subsequently formed by cell- 

 multiplication; the other pole only closing-in when a large number of 

 cells have been formed. The cells are then carried apart from one an- 

 other by the hyaline investment formed by each; and the characteristic 

 Vol vox-sphere is thus completed. 1 



241. There are other points in the life-history of Volvox which must 

 not be left without mention, although their precise import is as yet un- 

 certain. Thus, according to Mr. G. Busk (with whom Prof. Cohn is in 

 accord on this point), the body designated by Prof. Ehrenberg Splicero- 

 sira volvox is an ordinary Volvox in a different phase of development; its 

 only marked feature of dissimilarity being that a large proportion of 

 the green cells, instead of being single (as in the ordinary form of Vol- 

 vox}, save where they are developing themselves into young spheres, are 

 very commonly double, quadruple, or multiple; and the groups of ciliated 

 cells thus produced, instead of constituting a hollow sphere, form by 

 their aggregation discoid bodies, of which the separate fusiform cells are 

 connected at one end, whilst at the other they are free, each being fur- 

 nished with a single flagellum. These clusters separate themselves from 

 the primary sphere, and swim forth freely, under the forms which have 



1 The doctrine of the vegetable nature of Volvox, which has been suggested 

 by Siebold, Braun, and other German Naturalists, was first distinctly enunciated 

 by Prof. Williamson, on the basis of the history of its development, in the 

 "Transactions of the Philosophical Society of Manchester," Vol. ix. Subse- 

 quently Mr. G. Busk, whilst adducing additional evidence of the Vegetable 

 nature of Volvox, in his extremely valuable Memoir in the " Transactions of the 

 Microscopical Society," N. S., Vol. i. (1853), p. 31, called in question some of the 

 views of Prof. Williamson, which were justified by that gentleman in his " Fur- 

 ther Elucidations" in the same "Transactions." The description above given 

 by the Author, on the basis of the facts in which these excellent observers were 

 agreed (their original differences having been in great degree reconciled by their 

 mutual admissions), is in entire harmony with the most recent account of this most 

 interesting organism given by Prof. Cohn (" Beitrage zur Biologie der Pflanzen," 

 Bii. i., Heft 3, 1875), to whom we owe the discovery of its generative process. 

 The observations of Dr. Kirchner on its germination will be found in Bd. iii., 

 Heft 1 (1879), of the same serial. An extremely interesting Volvocine form de- 

 scribed by Cohn under the name Stephanosphcera pluvialis exhibits all the phe- 

 nomena of reproduction by macro-gonidia or composite masses of adherent cells, 

 by micro-gonidia or active zoospores, by ' still ' or stato-spores, and by oo-spores 

 produced by true sexual action, in a very characteristic manner; and his account 

 of its life-history should be consulted by every one who desires to study that of 

 any of the Protophyta. See "Ann. of Nat. Hist.," 3d Ser., Vol. x. (1852), pp. 331, 

 401, and " Quart. Journ. of Microsc. Sci.," Vol. vi. (1858), p, 131. 



