VOLVO CINE M 555 



been produced ; a similar envelope can he easily distinguished, as 

 shown in Xo. 10, just when the segmentation has been completed, 

 and at that stage the fiagella pass into it, but do not extend beyond 

 it ; and even in the mature Volvox it continues to form an invest- 

 ment around the hyaline envelopes of the separate cells, as shown in 

 the same figure at Ko. 11. It seems to be by the adhesion of the 

 hyaline investment of the new sphere to that of the old that the 

 xM-ondary sphere remains for a time attached to the interior wall of 

 the primary ; at what exact period, or in what precise manner, the 

 separation between the two takes [dace has not yet been determined. 

 At the time of the separation the developmental process has gene- 

 rally advanced as far as the stage represented in Xo. 1. the foundation 

 of one or more tertiary spheres being usually distinguishable in the 

 enlargement of certain of its cells. 



The development and setting-free of these composite zoosporanges, 

 which is essentially a process of cell-subdivision or gcniinii>(ircni.s exten- 

 sion, is the ordinary mode of multiplication in Volvox. taking place 

 at all times of the ye;ir. except when the sexual generation (now to 

 be described) is in progress. The mode in which this process i> 

 here performed (for our knowledge of which we are indebted to 

 the persevering investigations of Professor Colin) shows a great 

 advance upon the simple conjugation of tw T o similar cells, and 

 closely resembles that which prevails not only among the higher 

 algje, but (under some form or other) through a large part of the 

 cryptogamic series. As autumn advances the Volvo.r, spheres usually 

 cease to multiply themselves by the formation of zoosporanges, and 

 certain of their ordinary cells begin to undergo changes by which 

 they are converted, some into male or ' sperm-cells,' others into 

 female or ' germ-cells,' the greater number, however, remaining 

 sterile. Each sphere of Volvox ylobator (Plate VI, fig. 1) contains 

 both kinds of sexual cells, so that this species ranks as monoecious ; 

 but V. aureus is dioecious, the sperm-cells and germ-cells occurring 

 in separate spheres. Both kinds of sexual cells are at first dis- 

 tinguishable from the ordinary sterile cells by their larger size 

 (fig. 2, rt), in this respect resembling zoosporanges in an early 

 >t;ige; but their subsequent history is altogether different. The 

 sperm-cells begin to undergo subdivision when they attain about 

 three times the size of the sterile cells : this, however, takes 

 place, not on the binary plan, but in such a manner that the 

 eiidochrome of the primary cell resolves itself into a cluster of very 

 peculiar secondary cells (tig. 1, a, a 2 , fig. 5), each consisting of an 

 elongated 'body' containing an orange-coloured eiidochrome with a 

 red corpuscle, and of a long, colourless beak from the base of which 

 proceeds a pair of long flagella (tigs. (5, 7), as in the antherozoids 

 of the higher cryptogams. As the sperm-cells approach maturity, 

 the aggregate clusters may be seen to move within them, at first 

 slowly, and afterwards more rapidly; the bundles then separate 

 into their component antherozoids, wliich show an active, indepen- 

 dent movement whilst still within the cavity of the primary cell 

 (fig. 1, a 3 ), and finally escape by the giving-way of its wall ( 4 ), 

 diffusing themselves through the cavity of the Volvox sphere. The 



