CCENOBIE.^ 293 



or zoosporanges thus formed have the form and appearance of the 

 parent-colony, each segment possessing a single chlorophyll-body, which 

 contains starch. Ultimately, while still within the parent-colony, vibra- 

 tile cilia are developed in its peripheral segments, which cause it to 

 rotate, clothed at first by a transparent mucilaginous envelope, which 

 it at length breaks through. The number of colonies of zoospores thus 

 produced within the parent-colony is normally eight, resulting appa- 

 rently from the eight cells into which the parent-colony breaks up on 

 its third segmentation. The young colonies complete their growth in a 

 feW' days, attaining a diameter of from 100 to 150 mm., and have by 

 this time absorbed the greater part of the chlorophyll and starch of the 

 parent-colony, from which they finally escape. 



Volvox may multiply by this non-sexual mode of propagation for 

 several successive generations, and these are succeeded by a sexual mode 

 of reproduction. The male and female reproductive cells are formed 

 either in the same or in different colonies ; or, according to other ob- 

 servers, the so-called ' dioecious ' species are in reality proterandrous, 

 producing antherids at an earlier, oogones at a later stage. While the 

 non-sexual propagation by zoospores goes on through the whole year, the 

 sexual cells appear to be produced only in the autumn. The oogones are 

 at first quite indistinguishable from the non-sexual cells except in size, 

 but are much more numerous, and soon manifest a distinction from the 

 fact that they do not divide. On their first appearance they are about 

 three times the size of the sterile cells ; their protoplasm increases 

 rapidly, and becomes of a dark-green colour, from copious production 

 •of chlorophyll. They have at first a frothy appearance from the forma- 

 tion of vacuoles, but afterwards appear to be densely filled with the 

 dark-green endochrome. They soon become flask-shaped, the narrow 

 end touching the periphery of the colony, and the larger end hanging 

 free inside ; but, when ready for impregnation, round themselves off 

 into a spherical form, their contents being an oosphere enveloped bv a 

 gelatinous membrane. The antherids present at first sight a still closer 

 resemblance to zoospore-colonies at an early stage, but are lighter in 

 colour from containing a smaller quantity of chlorophyll. Their con- 

 tents soon begin to divide, but in two directions only, the young colony 

 thus developing into a plate instead of a sphere of segments enveloped 

 in a gelatinous coating. The colony ultimately resolves itself into a 

 bundle of antherozoids, naked fusiform masses of protoplasm, each 

 consisting of a thicker but elongated body, in which the chlorophyll has 

 been transformed into a yellow-brown pigment, and a slender colourless 

 beak, with a pigment-spot at its base, where also are attached on one 

 side two very long cilia. About the time when the oogones, with their 



