252 STRUCTURE OF VOLVOX GLOBATOR. 



been evolved ; their component particles, which are at first closely 

 aggregated together, being separated from each other by the inter- 

 position of the transparent pellicle. — It was long supposed that 

 the Volvox was a single Animal ; and it was first shown to be a 

 composite fabric, made up of a repetition of organisms in all 

 respects similar to each other, by Prof. Ehrenberg ; who, however, 

 considered these organisms as Monads, and described them as each 

 possessing a mouth, several stomachs, and an eye ! Our present 

 knowledge of their nature, however, leaves no doubt of their 

 Vegetable character ; and the peculiarity of their History readers 

 it desirable to describe it in some detail. 



194. Each of the so-called 'Monads' (Plate ix. Figs. 9, 11) is 

 in reality a somewhat flask-shaped mass of Endochrome, about 

 l-3000th of an inch in diameter ; consisting, as in the previous 

 instances, of Chlorophyll-granules diffused through a colourless 

 Protoplasm ; and bounded by a layer of condensed protoplasm, 

 which represents a Primordial Utricle, but is obviously far from 

 having attained a membranous consistence. It is prolonged out- 

 wardly (or towards the circumference of the sphere) into a sort of 

 colourless beak or proboscis, from which proceed two long vibratile 

 cilia (Fig. 11) ; and it is invested by a pellucid or Hyaline en- 

 velope (Fig. 9, d) of considerable thickness, the borders of which 

 are flattened against those of other similar envelopes (Fig. 5, c, c), 

 but which does not appear to have the tenacity of a true membrane. 

 It is impossible not to recognize the precise similarity between the 

 structure of this body, and that of the motile ' encysted ' cell of 

 Protococcus pluvialis (Plate vm. Fig. 2, k) ; there is not, in 

 fact, any perceptible difference between them, save that which 

 arises from the regular aggregation, in Volvox, of the cells which 

 normally detach themselves from one another in Protococcus. The 

 presence of Cellulose in the hyaline substance is not indicated, in 

 the ordinary condition of Volvox, by the iodine and sulphuric acid 

 test, though the use of 'Schultz's solution' gives to it a faint blue 

 tinge ; there can be no doubt of its existence, however, in the 

 hyaline envelope of what has been termed Volvox aureus, which 

 seems to be the sporangial form of Volvox globator (§ 199). The 

 cilia and endochrome, as in the motile forms of Protococcus, are 

 tinged of a deep brown by iodine, with the exception of one or 

 two particles in each cell, which, being turned blue, may be in- 

 ferred to be Starch ; and when the contents of the cell are libe- 

 rated, bluish flocculi, apparently indicative of the presence of 

 Cellulose, are brought into view by the action of sulphuric acid 

 and iodine. All these reactions are characteristically Vegetable in 

 their nature. — Vv'hen the cell is approaching maturity, its Endo- 

 chrome always exhibits one or more ' vacuoles ' (Fig. 9, a a), of a 

 spherical form, and usually about one-third of its own diameter ; 

 and these ' vacuoles ' (which are the so-called ' stomachs ' of Prof. 

 Ehrenberg) have been observed by Mr. Gr. Busk to undergo a very 



