VOLVOCINE.E. 63 



develop into plates or discs of cells, not into spheres, and ultimately 

 resolve themselves into bundles of naked elongated cells, in which the 

 chlorophyll is transformed into a reddish pigment, each with a long 

 colourless beak, with a red ' eye-spot ' and two cilia. (Plate 22, Fig. 

 oa, a 2 .) About the same time that the oosphere is mature these 

 antheridia begin to move from the combined action of their cilia (Plate 

 23, Fig. 10), and then break up into separate antherozoids, which finally 

 become free, and move rapidly within the cavity of the sphere. (Plate 

 23, Fig. 5a ! .) Assembling round the oospheres, they penetrate the 

 envelopes of the latter (Plate 22, Fig. 4), coalesce with their contents, 

 nnd the oosphere, thus fertilised, becomes an oospore, which soon develops 

 a cell-wall covered with conical stellate projections, and a second smooth 

 internal membrane. (Plate 23, Fig. 11.) The chloi-ophyll now gradually 

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

 the oospore constitutes the Volvocr 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 

 Micrographie," 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 months, 

 and in the following autumn the alternation of generations is again 

 completed by the intervention of the processes just described." 



Volvox globator. Linn. Syst. Ed. x. 



Larger ccenobia, with very numerous cells (12,000), always 

 with daughter- ccenobia enclosed within the mother, evolved 

 without sexuality ; fructification dioecious ; the male ccenobia 

 nourishing numerous red fascicles of spermatozoa ; the female 

 ccenobia originating 20-40 sexual cells, which after fecundation 

 are resolved into as many red globose oospores, surrounded by a 

 hyaline stellate epispore (=Volvox stellatus, Ehr.). 



SIZE. Ccenobium as much as 1 mm. diam. 



Ehrb. Infus. 68, t. 4. Dujardin Zoophy. 312, iii. f. 25. Stein 

 Infus. p. 46. Rabh. Alg. Eur. iii. 97. Pritchard Infus. 526, 

 t. 20, f. 32-47. Busk. Trans. Micr. Soc. 1853, p. 31. Wil- 

 liamson Trans. Micr. Soc. 1853, p. 45. Currey Ann. Nat. Hist. 

 1859, p. 5. Dr. J. B. Hicks in Micro. Journ. 1861, p. 281 ; in 



