STRUCTURE AND LIFE-HISTORY OF VOLVOX GLOBATOR. 45 



develop into pUites or discs of cells, )iot into spheres, and ultimately reaolve 

 themselves into bundles of naked elongated cells, in which the chloro- 

 phyll is transformed into a reddish pif^meut, each with a lonj^ colourless 

 beak, with a red " eye-spot" and two cilia. (Plate VIII, Fig. 1, a, «2.) 

 About the same time that the oo-sphere is mature these antheridia begin 

 to move from the combined action of their cilia, (Plate VIII., Fig. 2,) and 

 then break up into separate anthero:ioids, which finally become free and 

 move rapidly within the cavity of the sphere. (Plate VIII., Fig. 1, a.S.) 

 Assembling round the oo-spheres, they penetrate the envelopes of the 

 latter, (Plate VIII., Fig. .3,) coalesce with their contents, and the 

 oQ-splierc thus fertilised becomes an oospore, which soon develops a cell- 

 wall covered with conical stellate projections, and a second smooth internal 

 membrane. (Plate VIII., Fig. i.) The chlorophyll now gradually 

 disappears, and is replaced by an orange red pigment. In this condition 

 the oo-spore constitutes the Volvox stellatus of Ehrenberg. It is liberated 

 by the decay of the parent-cell, and sinks to the bottom of the water to 

 hibernate. The subsequent history of these bodies has been traced by 

 Cienkowski, and more recently by Henneguay, ("Journal de Micro- 

 graphie," Vol. II., p. 485, Bull. Soc. Philomath, Paris, July, 1878.) 



Cohn believed that they must be dried up before germination was 

 possible. Henneguay has now observed that this is not so. In spring 

 the outer case of the spore (exospore) is ruptured, and the swollen con- 

 tents (endospore) project through the opening. The contents then 

 divide gradually into two, four, eight, sixteen, or more small cells, which 

 become bright green, each meanwhile acquiring two vibratile cilia while 

 still contained within the inner membrane of the spore. The cells, at 

 first in close apposition, separate further from one another by interposi- 

 tion of gelatinous hyaline matter, the outer membrane disappears, the 

 cilia become active, and the young Volvox, already containing some 

 elements larger than the others and destined, in due course, to produce 

 daughter-spheres, moves freely through the water. " The spores of 

 Volvox, therefore, germinate in water, and each of them produces a single 

 colony by a process of segmentation identical with that which gives rise 

 to a daughter-colony at the expense of a cell of the mother-colony." 



The sequence of asexual generations is repeated for many mouths, 

 and in the following autumn the alternation of generations is again com- 

 pleted by the intervention of the processes just described. 



There are other phenomena of more or less exceptional occurrence 

 and of lesser interest in the history of Volvox, to which I might allude 

 did space permit, but those which I have traced constitute the essential 

 elements in the structure and life-history of this singularly beautiful and 

 interesting plant. I trust that I have succeeded in presenting to my 

 fellow-students a somewhat more complete and life-like account of them 

 than is accessible in ordinary text-books, and in showing how amply this 

 organism will repay careful and systematic observation. 



