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but it seems very probable that the ancestor combined the 

 faculty of zoospore-formation with that of ordinary vegetative 

 division. In Pleurococcus we have another example of a 

 simple organism of this type, but, as will be explained below, 

 it is probably more correct to regard this genus as a reduced 

 than as a primitive form. There are, therefore, among these 

 Protococcaceae, forms capable both of zoospore-formation and 

 vegetative division, and others able only to form zoospores. 

 It is interesting that the third possibility (that of an organism 

 capable only of vegetative division) is realised in the genus 

 Eremosphcera (Moore 51), a large spherical form very abundant 

 in the small pools of peat-bogs. Eremosphcera, however, differs 

 from the forms previously considered in having numerous dis- 

 coid chloroplasts, and its correct systematic position yet remains 

 to be settled. 



The methods of reproduction found in the Protococcaceae 

 (Klebs 37) are worthy of a brief consideration, as they give an 

 idea as to the possible origin of another line of algal descent. 

 In Chlorococcum the motile elements formed as a result of the 

 subdivision of the cell-contents appear to be purely asexual in 

 character, although it is not impossible that a sexual tendency 

 may yet be discovered in view of the behaviour of the motile 

 elements in the species of Chlorochytrium. In some of these 

 the motile elements are again asexual zoospores, but in others 

 they fuse in pairs, while still within the bladder which surrounds 

 them after liberation from the mother-cell (fig. 3A). This is no 

 doubt a very primitive type of sexual process, since gametes 

 from the same mother-cell are concerned in copulation, but it 

 is also interesting because there is practically no swarming- 

 stage prior to sexual fusion, although the zygozoospore sub- 

 sequently becomes liberated and moves actively to a new 

 host-plant. This restriction of swarming-power is much more 

 obvious in Endosphcera, in which the reproductive process is 

 a little more complicated. As in Chlorochytrium or Chlorococcum 

 the cell-contents undergo subdivision, but the products become 

 enveloped by cell-membranes even before cilia are formed and 

 without being liberated from the mother-cell, thus giving rise 

 to a multicellular individual. Each cell of the latter sub- 

 sequently liberates a number of isogametes. The chief interest 

 of the reproductive process of Endosphcera lies in the co-opera- 

 tion of all the zoospores, formed from a single mother-cell, 



