238 THE MICROSCOPE AtfD ITS REVELATIONS. 



and the contained spherules swim forth and speedily develop themselves 

 into the likeness of that within which they have been evolved; their 

 colored particles, which are at first closely aggregated together, being 

 separated from each other by the interposition of the transparent pellicle. 

 It was long supposed that the Volvox is 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 knowl- 

 edge of their nature, however, leaves little doubt of their Vegetable 

 character; 1 and the peculiarity of their history renders it desirable to 

 describe it in some detail. 



237. Each of the so-called ' monads' (Plate ix., figs. 9, 11) is a 

 somewhat flask-shaped Plant-cell, about l-3000th of an inch in diameter; 

 consisting, as in the previous instances, of green chlorophyll-granules 

 diffused through a colorless protoplasm, constituting an ( endochrome ' 

 (which commonly includes also a red spot of altered chlorophyll); and 

 bounded by an ( ectoplasm' formed of the condensed and * colorless 

 surface-layer of the protoplasmic mass. It is prolonged outwardly (or 

 towards the circumference of the sphere) into a sorb of colorless beak or 

 proboscis, from which proceed kwoflagella (fig. 11); and it is invested bv 

 a pellucid or hyaline envelope (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 vni., 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 them- 

 selves from one another in Protococcus. The presence of cellulose in the 

 hyaline substance is not indicated, in the ordinary condition of Volvox 

 globator, by the iodine and the 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 Volvox aureus 

 ( 240). The flagella and endoplasm, as in the motile forms of Protococ- 

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

 two starch-particles in each cell, which are turned blue; and when the 

 contents of the cell are liberated, 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. When the cell is approaching maturity, its endoplasm 

 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. G. Busk to undergo a very curious rhythmical contrac- 

 tion and dilatation at intervals of about 40 seconds; the contraction 

 (which seems to amount to complete obliteration of the cavity of the 

 vacuole) taking place rapidly or suddenly, whilst the dilatation is slow 



'Prof. Stein, however, in the last-published part of his great work on the 

 Infusoria (" Organismus der Infusionsthiere," Abtheilung in., Leipzig, 1878), still 

 ranks the Volvocinece among the Flagellate animalcules, to which they undoubt- 

 edly show a remarkable parallelism in structure, the chief evidence of their 

 Vegetable nature lying in their physiological conformity to undoubted Proto- 

 phytes. 



