240 THE MICROSCOPE AND ITS REVELATIONS, 



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 Protococcus, of a peculiar modification of chloro- 

 phyll. 



238. Each cell normally communicates with the cells in nearest prox- 

 imity with it, by extensions of its own endochrome, which are some- 

 times single and sometimes double (fig. 5, , #); and these connecting 

 processes necessarily cross the lines of division between their respective 

 hyaline investments. The thickness of these processes varies very con- 

 siderably; for sometimes they are broad bands, and in other cases mere 

 threads; whilst they are occasionally wanting altogether. This differ- 

 ence seems partly to depend upon the age of the specimen, 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 endochrome to a distance from one another (figs. 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 fig. 5), 

 or they retain their globular form, and the connecting processes alto- 

 gether disappear. The influence of re-agents, or the infiltration of 

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

 the connecting process (as in Protococcus, 231) to be drawn back into 

 the central mass of endochrome; and they will also retreat on the mere 

 rupture of the hyaline investment : from these circumstances it may be 

 inferred that they are not inclosed in any definite membrane. On the 

 other hand, the connecting threads are sometimes seen as double lines, 

 which seem like tubular prolongations of a consistent membrane, with- 

 out any protoplasmic granules in their interior. It is obvious, then, 

 that an examination of a considerable number of specimens, exhibiting 

 various phases of conformation, is necessary to demonstrate the nature 

 of these communications; but this may be best made-out by attending to 

 the history of their development, which we shall now describe. 



239. The spherical body of the young Volvox (Plate ix., fig. 1) is 

 composed of an aggregation of somewhat angular masses of endochrome 

 (b), separated by the interposition of hyaline substance; and the whole 

 seems to be inclosed in a distinctly membranous envelope, which is pro- 

 bably the distended hyaline investment of the ' primordial ' cell, within 

 which, as will presently appear, the entire aggregation originated. In 

 the midst of the polygonal masses of endochrome, one mass (), rather 

 larger than the rest, is seen to present a circular form; and this, as will 

 presently appear, is the originating cell of what is hereafter to become a 

 new sphere. The growing Volvox at first increases in size, not only by 

 the interposition of new hyaline substance between its component masses 

 of endochrome, but also by an increase in these masses themselves (fig. 

 2, #), which come into continuous connection with each other by the coa- 



1 The existence of rhythmically contracting vacuoles in Volvox (though con- 

 firmed 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. 



