STRUCTURE OF VOLVOX GLOBATOR. 261 



greater part of the coloring matter contracting into a small irre- 

 gular mass, which adheres to the bottom or side of the cell, 

 leaving the rest of the cavity clear and transparent), and the 

 formation of the red spot (6), which obviously coijsists, as in 

 Protococcus, of a peculiar modification of chlorophyll. 



159. Each mass of endochrome normally communicates with 

 those in nearest proximity with it, by extensions of its own sub- 

 stance, which are sometimes single and sometimes double (b, b 

 I); and these connecting processes necessarily cross the lines of 

 division between their respective hyaline investments. The 

 thickness of these processes varies very considerably ; for some- 

 times 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 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 (b, c, d); whilst in a mature individual, in 

 which this separation has taken place to its full extent, and the 

 nutritive processes have become less active, the masses of endo- 

 chrome very commonly assume an angular form, and the con- 

 necting processes are drawn out into threads (as seen at e), or 

 they retain their globular form, and the connecting processes 

 altogether disappear. The influence of reagents, or the infiltra- 

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

 sometimes cause the connecting processes (as in Protococcus, § 

 154), to be drawn back into the central mass of endochrome ; 

 and they will also retreat on the mere rupture of the hj'aline in- 

 vestment ; from these circumstances it may be inferred, that they 

 are not enclosed 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 de- 

 monstrate 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. 



160. The spherical body of the young Volvox (Fig. 78, a) is 

 composed of an aggregation of somewhat angular masses of en- 

 dochrome (6), separated by the interposition of hyaline substance ; 

 and the whole seems to be enclosed in a distinctly membranous 

 envelope, which is probably 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 {a), 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 



