PROFESSOR W. C. WILLIAMSON ON VOLVOX GLOBATOR. 323 



intercellular spaces being more or less transparent. After a 

 while, the green colouring matter changes its form, losing 

 its regularly angular aspect, and assuming the appearance 

 of Fig, 2 a. In this stage we cease to perceive the original 

 outlines of the cell ; but on the application of some re-agents 

 they can readily be brought into view. This irregularity of 

 form appears to arise from the existence of a ductile cell- 

 membrane which primarily lines the interior of each cell, 

 whilst it surrounds the cell-contents. This inner mem- 

 brane becomes separated from the outer cell wall, excepting 

 at a few points {Fig. 2 h), where it is retained in contact. 

 It now undergoes some curious changes, which alike aifect 

 its form and the character of its contents. 



After a time the angular projections of the inner mem- 

 branes of diflPerent cells appear to become still more inti- 

 mately united, as represented in Fig. 3 a. This appearance 

 seems to be caused by the further diminution of the con- 

 nection between the outer cell-wall and its internal cell or 

 lining membrane, from the shrinking of the latter tissue. 



Whilst these changes are in progress, an increase in the 

 diameter of the entire organism is taking place, unaccom- 

 panied by any corresponding addition to the number of the 

 cells, or to the amount of endochrome which they contain. 

 Hence the older organisms appear much more transparent 

 than the younger ones. Along with this general enlarge- 

 ment, there appears to be an increase in the diameter of the 

 individual cells ; but whether this is owing to a real disten- 

 sion of the outer cell-membrane, or merely to the flattening 

 of cells which were previously somewhat spherical, is doubt- 

 ful. I suspect that the former may be the case. It is 

 obvious that the superficial area of each cell enlarges ; and 

 as the projecting radii of the inner cell and its endochrome 

 retain their attachment to the outer cell-wall, the expansion 

 of the latter leads to an elongation of the former ; this is, 

 of course, accomplished at the expense of the central 



