556 MICROSCOPIC FORMS OF VEGETABLE LIFE THALLOPHYTES 



<7erm-cells (fig. 1, b, 6), on the other hand, continue to increase in 

 size without undergoing subdivision ; at first showing large vacuoles 

 in their protoplasm (6 2 , & 2 ), but subsequently becoming filled with 

 dark-green endochrome. The form of the germ-cell gradually 

 changes from its original flask-shape to the globular (6 3 ) ; and it 

 projects into the cavity of the Volvox sphere, at the same time 

 acquiring a gelatinous envelope. Over this the swarming antherozoids 

 diffuse themselves (fig. 3), penetrating its substance, so as to find 

 their way to the interior ; and in this situation they seem to dissolve 

 away, so as to become incorporated with the oosphere. The product 

 of this fusion (which is only conjugation under another form) is a 

 reproductive cell or oospore, 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 Palmoglcea, to starch 

 and a red or orange coloured oil. As many as forty of such oospores 

 have been seen by Cohn in a single sphere of Volvox, which thus 

 acquires the peculiar appearance that has been distinguished by 

 Ehrenberg by a different specific name, Volvox stellatus. Soon 

 after the oospores reach maturity, the parent sphere breaks up, 

 and the oospores fall to the bottom, where they remain during 

 the winter. 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 each 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 another by 

 the hyaline investment formed by each, and the characteristic Volvox 

 sphere is thus completed. 1 



Another phenomenon of a very remarkable nature, namely, the 

 conversion of the contents of an ordinary vegetable cell into a free 

 moving mass of protoplasm that bears a strong resemblance to the 

 animal Amceba, has been affirmed by Dr. Hicks 2 to take place in 

 Volvox, under circumstances that leave no reasonable ground for that 

 doubt of its reality which has been raised in regard to the accounts 

 of similar phenomena occurring elsewhere. The endochrome-mass of 

 one of the ordinary cells increases to . nearly double its usual size ; 

 but, instead of undergoing binary subdivision so as to produce a 

 zoosporange, it loses its colour and its regularity of form, and 



The doctrine of the vegetable nature of Volvox, which had 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. 



[The most recent and detailed accounts of the development of the various forms 

 of Volvox are by Klein (Pringsheim's Jahrbucher fur wissenschaftliche Botanik, 

 vol. xx. 1889, p. 133) and Overtoil (Botanisches Centralblatt, vol. xxxix. 1889), which 

 do not differ in any material point from the description given in the text. See also 

 Bennett and Murray's Handbook of Cryptogamic Botany, p. 292. ED.] 



2 Trans, of Microsc. Society, n.s. vol. viii. 1860, p. 99 ; and Quart. Jo-urn, of 

 Microsc. Science, n.s vol. ii. 1862, p. 96. 



