DEVELOPMENT OF VOLVOX 6L0BAT0E. 263 



globular cell lias undergone segmentation into two halves. In 

 the stage represented at d, the masses of endochrome have been 

 still more widely separated by the interposition of hyaline sub- 

 stance ; each has become furnished with its pair of ciliary fila- 

 ments; and the globular cell has undergone a second segmenta- 

 tion. Finally at e, which represents a portion of the sphei'ical 

 wall of a mature Volvox, the endochrome 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 ordinary cells to their primordial utricle, is 

 frequently seen to be marked out from the rest by delicate lines 

 of hexagonal areolation (c, e), which indicate the boundaries of 

 each. Of these it is often difficult to obtain a sight, a nice 

 management of the light being usually requisite with fresh spe- 

 cimens; but the prolonged action of water (especially when it 

 contains a trace of iodine), or of glycerine, 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 some- 

 times retreat from each other so far, that the hexagonal areolae 

 become rounded. 



161. As the primary sphere approaches maturity, the second- 

 ary germ, whose origin has been traced from the beginning, also 

 advances in development; its contents undergoing multiplica- 

 tion by successive segmentations, so that we find it to consist ot 

 8, 16, 32, 64, and still more numerous divisions, as shoWn in 

 Fig. 70, F, G, H. Up to this stage, at which first the sphere 

 appears to become hollow, it is retained within the hyaline enve- 

 lope of the cell within which it has been produced ; a similar 

 envelope can be easily distinguished, as shown at k, just when 

 the segmentation has been completed, and at that stage the cilia 

 pass into it, but do not extend beyond it; and even in the 

 mature volvox, it continues to form an investment around the 

 hyaline envelopes of the separate cells, as shown at L. 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 developmental process has generally 

 advanced as far as the stage represented at a ; the foundation of 

 one or more tertiary spheres being usually distinguishable in the 

 enlargement of certain of its cells. And thus the cycle of 

 development is completed, in so far as regards the increase of 

 cells by subdivision. But, as already pointed out, the life-his- 

 tory of no organism can be considered as complete, unless it 



