STRUCTURE AND LIFE-HISTORY OF VOLVOX GLOBATOR. 235 



the actual formative matter of the sphere receives no further, or only a 

 disproportionate increment, but is gradually attenuated by continued 

 expansion, as a soap bubble is distended by blowing into it, the hexagonal 

 lines into which it has been moulded by the previous mutual pressure 

 of the embryo gonidia will be gradually stretched in all directions into 

 finer proportions ; and just as this figure is that which is necessarily 

 assumed by a number of spherical bodies under mutual pressure, so the 

 most economical disposition of this particular part of the Volvox-structure 

 will necessitate its constant attenuation into hexagons of ever-increasing 

 delicacy. (Plate VII., Figs. 1, 3, 7.) If the process be continued long 

 enough, it may finally result in the structure becoming too filmy to be 

 detected by any microscopical observation ; and it is worth noticing that 

 it is usually in spheres of small or medium diameter that the hexagonal 

 divisions can be developed, and ,not in those of the largest size. Such 

 appears to me at present to be the rationale of the formation of this 

 structure. 



The internal cavity of the sphere is said to be filled with a 

 "mucilaginous fluid." If a Volvox be ruptured under a cover-glass, and 

 aniline purple introduced by capillary attraction, the colour seems to be 

 for awhile repelled at that part which is in front of the rupture, and to 

 flow round it on either side. It is only after a considerable time that it 

 gradually penetrates this space, and brings out, by staining it of a deep 

 purple tint, a mass of hazy matter, from which proceeds streaks or lines, 

 radiating more or less regularly from its south pole. (Plate VII., Fig. 6.) 

 This structure, to which I do not think attention has been hitherto 

 called, is also sometimes developed in deeply-stained specimens within 

 the slightly ruptured sphere, and seems to show that there is a denser 

 layer of thick matter, whatever its nature may be, disposed in a some- 

 what regular manner, being concentrated near the south pole of the axis 

 of rotation, whence it spreads over the inner surface in streaks resembling 

 the lines of longitude on a terrestrial globe. 



Both from its position and from the rapidity with which it is stained 

 by aniline purple — without which its existence is apparently absolutely 

 undemonstrable — (in which respect it is in marked contrast to the outer 

 cell-wall, which latter is only faintly tinted by somewhat prolonged 

 application of the re-agent, and then only where the hexagonal structure 

 exists,) I have no doubt that this inner layer is the true " primordial 

 utricle " of the cell, and possesses that character of vital and formative 

 matter which distinguishes this element of cell-structure from the outer 

 wall, which, on the other hand, probably consists of cellulose or some 

 similar compound. Probably the arrangement of this inner layer in 

 radiating lines or ribs contributes to the elasticity of the fabric, whereby 

 it it enabled to open at a given point for the escape of the young, and to 

 contract again after their emission. 



The increase of individuals by the means already described is strictly 

 an instance of subdivision. 



But Volvox Globator also affords an instance of true alternation of 

 generations. As may probably be affirmed of all living organisms, its 



