552 MICROSCOPIC FORMS OF VEGETABLE LIFE- Til ALLOPHYTES 



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 ylobator, 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 Volvox aureus. The flagella 

 and endoplasm, as in the motile forms of Protococcus, are tinged 

 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 endo- 

 plasm always exhibits one or more vacuoles (fig. 421, No. 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 Ehrenberg) 

 have been observed to undergo a very curious rhythmical contraction 

 and dilatation at intervals of about forty 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 

 and gradual. This curious action ceases, however, as the cell 

 arrives at its full maturity ; 1 a condition which seems to be 

 marked by the greater consolidation of the ectoplasm, by the 

 removal or transformation of some of the chlorophyll, and by the 

 formation of the red spot (&), which obviously consists, as in Proto- 

 coccus, of a peculiar modification of chlorophyll. 



Each cell normally communicates with the cells in nearest 

 proximity with it by extensions of its own endochrome, which are 

 sometimes single and sometimes double (fig. 421, No. 5, b, b) ; and 

 these connecting processes necessarily cross the lines of division 

 between their respective hyaline investments. The thickness of these 

 processes varies very considerably ; for sometimes they are broad 

 bands, and in other cases mere threads ; whilst they are occasionally 

 wanting altogether. This difference seems partly to depend upon the 

 age of the individual, and partly upon the abundance of nutriment 

 which it obtains ; for, as we shall presently see, the connection is 

 most intimate at an early period, before the hyaline investments of 

 the cells have increased so much as to separate the masses of endo- 

 chrome to a distance from one another (fig. 421, Nos. 2, 3, 4) ; whilst 

 in a mature individual, in which the separation has taken place to 

 its full extent and the nutritive processes have become less active, the 

 masses of endochrome very commonly assume an angular form, and 

 'the connecting processes are drawn out into threads (as seen in No. 5), 

 or they retain their globular form, and the connecting processes 

 altogether disappear. The influence of reagents, or the infiltration 

 of water into the interior of the hyaline investment, will sometimes 

 cause the connecting processes (as in Protococcus) to be drawn back 



1 The existence of rhythmically contracting vacuoles in Volvox (though confirmed 

 by the observations of Prof. Stein) is denied by Mr. Saville Kent (Manual of the 

 Infusoria, p. 47) ; but it may be fairly presumed that he has not looked for them at 

 the stage of development at which their action was witnessed by Mr. Busk. 



