MICROSCOPIC FORMS OF VEGETABLE LIFE. 



23T 



endochrome of one cell passes over entirely into the cavity of the other; 

 and it is within the latter that the 'zygospore' is formed (c), the two 

 endochromes coalescing into a simple mass, around which a firm envelope 

 gradually makes its appearance. Further, it may be generally observed 

 that all the cells of one filament thus empty themselves, whilst all the cells of 

 the other filament become the recipients: here, therefore, we seem to 

 have a foreshadowing of the sexual distinction of the Generative cells into 

 ' sperm-cells ' and 'germ-cells/ which we shall presently see in the fila- 

 mentous Confervacece. Multiplication by * zob'spores ' has not been seen 

 to take place among the Conjugates. 



236. From the composite ' motile ' forms of Proctococcus ( 232), the 

 transition is easy to the group of Volvocinece an assemblage of minute 

 Plants of the greatest interest to the Microscopist, on account both of 

 the Animalcule-like activity of their movements, and of the great beauty 

 and regularity of their forms. The most remarkable example of this 

 group is the well-known Volvox globator (FKONTSPIECE), which is not 



Various stages of the history of Zygnema quininum:^ three cells a, &, c, of a young filament 

 of which b is undergoing subdivision; B. two filaments in the first stage of conjugation, snowing- 

 the spiral disposition of their endochromes, and the protuberances from the conjugating cells; c, 

 completion or the act of conjugation, the endochromes of the cells of the filament a having entirely 

 passed over to those of filament 6, in which the zygospores are formed. 



uncommon in fresh-water pools, and which, attaining a diameter of 

 about l-50th or even l-30th of an inch, may be seen with the naked eye 

 when the drop containing it is held up to the light, swimming through 

 the water which it inhabits. Its onward motion is usually of a rolling 

 kind; but it sometimes glides smoothly along, without turning on its 

 axis; whilst sometimes, again, it rotates like a top, without changing its 

 position. When examined with a sufficient magnifying power, the 

 Volvox is seen to consist of a hollow sphere, composed of a very pellucid 

 material, which is studded at regular intervals with minute green spots, 

 and which is often (but not constantly) traversed by green threads con- 

 necting these spots together. From each of the spots proceed two long 

 flagella; so that the entire surface is beset with these lashing filaments, 

 to whose combined action its movements are due. Within the external 

 sphere may generally be seen from two to twenty other globes, of a darker 

 color, and of varying sizes; the smaller of these are attached to the inner 

 surface of the investing sphere, and project into its cavity; but the larger 

 lie freely within the cavity, and may often be observed to revolve by the 

 agency of their own flagella. After a time, the original sphere bursts, 



