554 MICROSCOPIC FOKMS OF VEGETABLE LIFE THALLOPHYTES 



composed of an aggregation of somewhat angular masses of endochrome 

 (6), separated by the interposition of hyaline substance ; and the 

 whole seems to be enclosed in a distinctly membranous envelope, 

 which is probably the distended hyaline investment of the original 

 cell, within which, as will presently appear, the entire aggregation 

 originated. In the midst of the polygonal masses of endochrome, 

 one mass (a), rather larger than the rest, is seen to present a 

 circular form ; and this, as will presently appear, is the originating 

 cell of what is hereafter to become a new sphere. The growing 

 Volvox at first increases in size not only by the interposition of new 

 hyaline substance between its component masses of endochrome, 

 but also by an increase in these masses themselves (No. 2, a), which 

 come into continuous connection with each other by the coalescence 

 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 

 preliminary to its binary subdivision. A more advanced stage of 

 the same developmental process is seen in No. 3, in which the con- 

 necting processes (a, a) have so much increased in size as to establish 

 a most intimate 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 undergone segmentation into two halves. 

 In the stage represented in No. 4 the masses of endochrome have 

 been still more widely separated by the interposition of hyaline 

 substance ; each has become furnished with its pair of flagella, and 

 the globular cell has undergone a second segmentation. Finally, in 

 No. 5, which represents a portion of the spherical 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 endo- 

 chrome mass in the relation of the cellulose coat of an ordinary cell 

 to its ectoplasm, 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 management 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 glycerin will often bring them into 

 clear view. The prolonged action of glycerin, 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 areolse become rounded. 

 As the primary sphere approaches maturity, the large secondary 

 germ-mass, or zoosporange, whose origin has been traced from the 

 beginning, also advances in development, its contents undergoing 

 multiplication by successive segmentations, so that we find it to 

 consist of eight, sixteen, thirty-two, sixty-four, or still more 

 numerous divisions, as shown in fig. 421, Nos. 6, 7, 8. Up to this 

 stage, at which the sphere first appears to become hollow, it is 

 retained within the hyaline envelope of the cell within which it has 



