THE VOLVOCIIvME 213 



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,fuseswith themacrogamete,and the result is 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 Volvocinae, the transition from the uni-cellular to the 

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

 specially important to note that certain members of the group, 

 Bodo angustatus is an example, are able to assume an amoeboid 

 stage and to return again to the flagellate condition. Others, 

 of which the genera Mastigamoeba and Mastigina are examples, 

 bear a typical flagellum but also put forth pseudopodia like 

 a Rhizopod. When we consider further that the young of 

 Badhamia and also the young of many Heliozoa (though not 

 of Actinosphaerium) are flagellate, we recognise that there is 

 no sharp dividing line between the Rhizopoda and the Flagel- 

 lata; the one form is capable of passing into the other, and 

 there can be little doubt that they stand in the closest relation- 

 ship to one another. Again, we see in the Flagellata organisms 

 which are exclusively holophytic and indistinguishable from 

 plants, organisms which are holozoic, and therefore unquestion- 

 ably animals, and organisms which are saprophytic, and there- 

 fore 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 Flagellata represent the group from which both animals 

 and plants have sprung, but this we can hardly do. Were 



