AFFINITIES OF FLAGELLATA 185 



repeatedly, in much the same manner as in Eudorina, to 

 form a flat plate or bundle of as many as 128 flagellate 

 spindle-shaped microgametes. In Volvox globator the bundle 

 now breaks up (the case is somewhat different in the closely 

 related Volvox minor) and the microgametes pass into the 

 central cavity of the colony. They swim by means of their 

 flagella towards a macrogamete, and bore their way into its thick 

 envelope. A single microgamete having passed through the 

 envelope, fuses with the macrogamete, and the resultis a fertilised 

 ovum or zygote. The zygote surrounds itself with a double 

 cyst-wall, not composed of cellulose, the outer wall being red 

 and provided with spines and projections. The zygote itself 

 forms a large number of starch granules in its protoplasm. A 

 long period of winter rest follows, and in the spring the zygote 

 develops by a repeated process of cell-division into a new 

 Volvox colony. 



The Flagellata are perhaps the most instructive group of 

 the Protozoa. On the one hand they are connected with the 

 lowliest forms of life, on the other hand they indicate, through 

 the Volvocinse, the transition from the uni-cellular to the 

 multi-cellular condition, from Protozoa to Metazoa. It is 

 specially important to note how many members of the group 

 are able to assume an amoeboid stage and to return again to the 

 flagellate condition. We have seen this to be the case in Bodo 

 angustatus, but there are many other instances, the best known 

 being a form called Mastigamceba, which passes regularly from 

 the flagellate to the amoeboid, and from the amoeboid back to 

 the flagellate condition again. When we consider further that 

 the young of Badhamia and also the young of many Heliozoa 

 (though not of Actinosphserium) are flagellate, we recognise that 

 there is no sharp dividing line between the Rhizopoda and 

 the Flagellata; the one form is capable of passing into the 

 other, and there can be little doubt that they stand in the 

 closest relationship to one another. Again, we see in the 

 Flagellata organisms which are exclusively holophytic and 

 undistinguishable from plants, organisms which are holozoic, 

 and therefore unquestionably animals, and organisms which are 

 saprophytic, and therefore resemble Fungi. We stand, as it 

 were, in neutral territory, belonging to neither the animal nor 

 to the vegetable kingdom, but inhabited by the natives of 

 both. It is tempting to suppose that the Flagellates represent 



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