24:2 THE MICROSCOPE AND ITS REVELATIONS. 



severing investigation of Prof. Colin 1 ) shows a great advance upon the- 

 simple ' conjugation ' of two similar cells ( 229), and closely resembles 

 that which prevails not only among the higher Alga, but (under some 

 form or other) through a large part of the Cryptogamic series. As 

 autumn advances, the Volvox-spheres usually cease to multiply them- 

 selves by the formation of * macro-gonidia; ' 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 globator 

 (FRONTISPIECE, fig. 1) contains both kinds of sexual cells, so that this 

 species ranks as monoecious; but V. aureus is diceciotis, the 'sperm-cells' 

 and 'germ-cells' occurring in separate spheres. Both kinds of 'sexual' 

 cells are at first distinguishable from the ordinary 'sterile' cells by 

 their larger size (fig. 2, a), in this respect resembling 'macro-gonidia' 

 in an early stage; 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 endochrome of the 

 primary cell resolves itself into a cluster of very peculiar secondary cells 

 (fig. 1, #, a 2 , fig. 5), each consisting of an elongated 'body' containing 

 an orange-colored endochrome with a red corpuscle, and of along color- 

 less beak, from the base of which proceeds a pair of long flagella (figs. 

 6, 7), as in the ' antherozoids ' of the higher Cryptogams (Fig. 154, H). 

 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 ' anterozoids,' which 

 show an active independent movement whilst still within the cavity of 

 the primary cell (fig. 1, a 8 ); and finally escape by the giving- way of its 

 wall (a 4 ), diffusing themselves through the cavity of the Volvox-sphere. 

 The germ-cells (fig. 1, b, b), on the other hand, continue to increase in 

 size without undergoing subdivision; at first showing large vacuoles in 

 their protoplasm (2 2 , # 2 ), but subsequently becoming filled with dark- 

 green endochrome. The form of the ' germ-cell ' gradually changes from 

 its original flask-shape to the globular (& 3 ); and it projects into the cav- 

 ity of the Volvox-sphere, at the same time acquiring a gelatinous envel- 

 ope. Over this the swarming antherozoids diffuse themselves (fig. 3),. 

 penetrating its substance, so as to find their way to the interior; and in 

 this situation they seem to dissolve-away, so as to become incorporated 

 with the endochrome. The product of this fusion (which is only ' con- 



1 The original observations of Colin on the sexuality of Volvox, published in 

 the "Ann. des Sci. Nat.," 4ieme Ser., Botan., Tom. v. (1857), p. 323, were con- 

 firmed by Mr. Carter, "Ann. Nat. Hist.," 3d Ser., Vol. iii. (1859), p. 4, who ob- 

 served the sexual process in Eudorina also. In the well-known form Pandorina 

 morum, the generative process is performed, according to the observations of 

 Pringsheim, in a manner curiously intermediate between the lower and the 

 higher types referred to above. For within each cell of the original sixteen of 

 which its mulberry-like mass is composed, a brood of sixteen secondary cells 

 is formed by ordinary binary subdivision; and these, when set free by the dis- 

 solution of their containing cell-wall, swim forth as ' swarm-spores,' each being fur- 

 nished with a pair of flagella. Among the crowd of these swarm-spores may be 

 observed some which approach in pairs, as if seeking one another; when they 

 meet, their points at first come together, but gradually their whole bodies coa- 

 lesce ; and a globular * zygospore ' is thus formed, which germinates after a period 

 of rest, reproducing by binary subdivision the original sixteen-celled mulberry- 

 like Pandorina. (See Sachs' "Botany," p, 219.) 



