EUPHYCOPHYTA 3I 



The majority of the cells, including all those in the anterior 

 quarter, are wholly somatic, and only a few are able to give rise to 

 daughter colonies or gametes. As the plant matures some of the 

 posterior cells enlarge and lose their flagellae. These are the poten- 

 tial reproductive cells. When daughter colonies are to be formed 

 the enlarged gonidium divides longitudinally a number of times 

 and a small hollow sphere is produced with a pore (phialopore) to- 

 wards the outer edge. These coenobia, which hang down into the 

 parent cavity, then invert, the process commencing opposite the 

 phialopore. After inversion flagella are formed and the colonies 

 may be liberated into the parental cavity or they may escape to the 

 exterior (Fig. 9). If retained they remain until the parent tears open, 

 in some species ( V. aureus) at the adult phialopore, in other species 

 ( V. glohator) at any place. In V, africana it is possible to see as many 

 as four generations in the one original parent colony, because the 

 original parent takes a long time before it breaks down. 



In sexual reproduction the plants are either monoecious {V, 

 glohator) or dioecious ( V, aureus). Cells becoming ova enlarge con- 

 siderably but do not imdergo division and the flagella disappear. 

 Cells giving rise to antherozoids divide to give bowl-shaped or 

 globose colonies containing 16, 32, 64, 128, 256 or 512 spindle- 

 shaped, biflageUate antherozoids. Both bowls and spheres undergo 

 inversion before maturation (cf. Fig. 10). The fertiHzation mechan- 

 ism is not known for certain, but in the dioecious species the 

 antherozoids are said to penetrate the female colony and then enter 

 the ovum from the inner side. Zygotes do not germinate for a con- 

 siderable time after Hberation. The first division involves meiosis 

 but the oospore produces a single swarmer that is Hberated into a 

 vesicle formed by extrusion of the inner oospore wall (endospore). 

 This grows into a *juvenile' plant of about 128 to 500 cells, which 

 finally inverts. It subsequently reproduces by daughter colonies, 

 each successive generation having an increased number of cells 

 (see p. 44 for comparison with Hydrodictyori) until a fully de- 

 veloped colony is produced. 



One of the features of this genus are the inversions that occur at 

 different stages of the Ufe-cycle, and it is difficult to see why they 

 occur or what the conditions were under which they first developed. 

 It may be associated with the fact that the new cells are formed with 

 the eye-spot facing the interior, but even then the problem arises 

 as to how the individual cells came to be arranged thus. Since the 



