276 -THE MICROSCOPE. 



tain stages in the history of their lives, are but the motile 

 forms {Zoospores) of some other plants, whose relation to 

 them is at present unknown." Professor Williamson, 

 having carefully examined the Volvox globator, says : — 

 " That the increase of its internal cells is carried on in a 

 manner precisely analogous to that of the algse; that 

 between the outer integument and the primordial cell- wall 

 of each cell, a hyaline membrane is secreted, causing the 

 outer integument to expand; and as the primordial cell- 

 wall is attached to it at various points, it causes the inter- 

 nal colouring- matter, or endochrome, to assume a stellate 

 form (see Plate I. No. 15), the points of one cell being in 

 contact with those of the neighbouring cell, these points 

 forming at a subsequent period the lines of communication 

 between the green spots generally seen within the full- 

 grown Volvox." Cilia can be distinctly seen on the outer 

 edge of the adult Volvox ; by compressing and rupturing 

 one, they may even be counted. Professor Busk has been 

 able to satisfy himself, by the addition of the chemical 

 test iodine, of the presence of a very minute quantity of 

 starch in the interior of the Volvox, which he considers 

 as conclusive of their vegetable character. A singular 

 provision is made in the structure of the gemmules, con- 

 sisting of a slender elastic filament, by which each is at- 

 tached to the parent cell- wall : at times it appears to thrust 

 itself out, as if in search of food ; it is then seen quickly to 

 recover its former nestling-place by contracting the tether. 

 It is impossible not to recognize the great similarity 

 between the structure of Volvox, and that of the motile 

 cell of Protococcus pluvialis. The influence of re-agents 

 will sometimes cause the connecting processes of the young 

 cells as in Protococcus, to be drawn back into the central 

 mass, and the connecting threads are sometimes seen as 

 double lines, which seem like tubular prolongations of a 

 consistent membrane. At other times they appear to be con- 

 nected by star-like prolongations to the parent cell, Plate I. 

 No. 15, presenting an almost identical appearance with 

 Pediastrum pertusum. Mr. Busk says that the body 

 designated by Ehrenberg Sp/icerosira volvox is an ordinary 

 volvox in a different phase of development; its only 

 marked feature of dissimilarity being that a large proper- 



