MICROSCOPIC FORMS OF VEGETABLE LIFE. 241 



lescence of processes (b) which they severally put-forth; at the same time 

 an increase is observed in the size of the globular cell (c), which is pre- 

 liminary to its binary subdivision. A more advanced stage of the same 

 developmental process is seen in fig. 3; in which the connecting pro- 

 cesses (a, a) are so much increased in size, as to establish a most in- 

 timate union between the masses of endochrome, although the increase 

 of the intervening hyaline substance carries these masses apart from one 

 another; whilst the endochrome of the central globular cell has under- 

 gone segmentation into two halves. In the stage represented in. fig. 4, 

 the masses of endochrome have been still more Avidely separated by the 

 interposition of hyaline substance; each has become furnished with its 

 pair of flagella; and the globular cell has undergone a second segmenta- 

 tion. Finally, in fig. 5, which represents a portion of the spherical wall 

 of a mature Volvox, the endochome-masses are observed to present a 

 more scattered aspect, partly on account of their own reduction in size, 

 and partly through the interposition of a greatly-increased amount of 

 hyaline substance, which is secreted from the surface of each mass; and 

 that portion which belongs to each cell, standing to the endochrome- 

 mass in the relation of the cellulose coat of an ordinary cell to its ecto- 

 plasm, is frequently seen to be marked-out from the rest by delicate lines 

 of hexagonal areolation (c, c) which indicate the boundaries of each. 

 Of these it is often difficult to obtain a sight, a nice arrangement of the 

 light being usually requisite with fresh specimens; but the prolonged 

 action of water (especially when it contains a trace of iodine), or of gly- 

 cerine, will often bring them into clear view. The prolonged action of 

 glycerine, moreover, will often show that the boundary lines are double, 

 being formed by the coalescence of two contiguous cell- walls; and they 

 sometimes retreat from each other so far that the hexagonal areolae be- 

 come rounded. As the primary sphere approaches maturity, the large 

 secondary germ-mass, or macro-gonidium, whose origin has been traced 

 from the beginning, also advances in development; its contents under- 

 going multiplication by successive segmentations, so that we find it to con- 

 sist of 8, 16, 32, 64, and still more numerous divisions, as shown in figs. 

 6, 7, 8. Up to this stage, at which first the sphere appears to become 

 hollow, it is retained within the hyaline envelope of the cell within 

 which it has been produced; a similar envelope can be easily distin- 

 guished, as shown in fig. 10, just when the segmentation has been com- 

 pleted, and at that stage the flagella 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 

 fig. 11. It seems to be by the adhesion of the hyaline investment of the 

 new sphere to that of the old, that the secondary 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 place, 

 has not yet been determined. At the time of the separation, the devel- 

 opmental process has generally advanced as far as the stage represented 

 in fig. 1 ; the foundation of one or more tertiary spheres being usually 

 distinguishable in the enlargement of certain of its cells. 



240. The development and setting-free of these composite 'macro- 

 gonidia,' which is essentially a process of cell-subdivision or gemmiparous 

 extension ( 226), is the ordinary mode of multiplication in Volvox; 

 taking place at all times of the year, except when the sexual generation 

 (now to be described) is in progress. The mode in which this process is 

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

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