STRUCTUEE AND LIFE-HISTORY OF VOLVOX GLOBATOR. 209 



ON THE STKUCTURE AND LIFE-HISTORY OF 

 VOLVOX GLOBATOR. * 



BY A. W. WILLS, F.C.S. 



No single organism in Nature has more frequently excited 

 transient feelings of admiration or interest than Volvox globator. In 

 the household or at public displays of microscopic objects, none more 

 often elicits expressions of wonder and delight. The exquisitely pure 

 green of its translucent spheres, their inimitable symmetry, and, above 

 all, the perfect grace of movement in a group of these plants, gliding 

 hither and thither with a methodical and stately rotatory motion, 

 passing and repassing, threading their way between one another, the 

 easy regularity of their courses never interrupted by collision, but only 

 checked for a moment when they approach too nearly, and then 

 instantly l'esumed ; in addition, the entire absence of any apparent 

 actuating force to account for this motion; — all these things combine 

 to make Volvox an object of unsurpassed beauty and of perennial delight. 

 Indeed, the microscopist can offer no more attractive spectacle than that 

 of a group of Volvox-spheres, young and old, seen under a low power 

 of his instrument, by a well-adjusted dark back-ground illumination. 



Yet it is an undoubted fact that the details of their more intimate 

 structure are unknown even to the majority of professed mioroscopists, 

 chiefly, no doubt, because they can only be revealed by the careful use of 

 somewhat high powers, assisted by the action of various re-agents. 



Finding that the descriptions given in ordinary text-books were 

 often too meagre to be of much value, and as often hopelessly obscure, I 

 was led to consult carefully the original memoirs of Cohn, Busk, 

 Williamson, &c, on this subject, and, wherever it was possible, to repeat 

 their observations — and having acquired by this means a far clearer idea 

 of the structure of Volvox than I had hitherto possessed, having also, 

 perhaps, added some few new facts to the common stock of such 

 knowledge, I have thought that a short summary of what is known 

 of its life-history might be of some use to my fellow-students. 



References to Plate VII. 



Fig. 1.— Mature Volvox sphere, showing daughter-spheres within, these also 



containing the enlarged gonidia, from which spheres of the third 



generation are to be derived ; also showing hexagonal structure and 



connecting threads. 

 Fig. 2.— Portion of Volvox sphere treated by glycerine, after Williamson. 

 Fig. 3,— Portion of Volvox sphere after treatment with solution of aniline 



purple. 

 Fig. 4, a toe.— Develapment of young Volvox from selected gonidia within 



the parent ; a to e— the same seen in section. 

 Fig. 5.— Probable section of portion of living Volvox, after Williamson. 

 Fig. 6.— Volvox ruptured under pressure, and treated by aniline purple, 



showing radiating streaks of primordial utricle. &c. 

 Fig. 7.— Portion of cell wall, showing the pores through which the cilia 



protrude. 



* Read before the Birmingham Natural History and Microscopical Society, 

 May 18th, 1880. 



