VITALITY 503 



gametes are one-eighth as large and are formed by three successive 

 divisions of the microgametocytes (Fig. 210). The microgametes 

 always become detached and swim about actively until they perish 

 or meet and fuse with a macrogamete. 



Amongst the Phytomonadida, the Volvocidse illustrate every tran- 

 sition from isogamy to complete anisogamy of egg and sperm, the 

 t^-jDC being distinguished as oogamy. Here the genera Eudorina, 

 Pleodorina and Volvox show real sexuality, eggs and spermatozoa 

 being formed, in some cases in sexually differentiated colonies. 

 According to the investigations of Goroschankin (1875), Goebel 

 (1882), Chatton (1910) and IMerton (1808) male and female colonies 

 are differentiated in Eudorina and Pleodorina. Egg cells of the 

 female colonies are only slightly different from the usual vegetative 

 cells. In the males the cells become highly modified; all cells of the 

 male colony, with the exception of the most anterior, become 

 gametocytes which divide as though forming daughter colonies 

 but the usual 82 gametes remain in a (Tonium-Yike plate. Their 

 color changes from green to yellow and they develop 2 ffagella and 

 become much elongated. Volvox, in the main, agrees with Eudorina. 

 In V. glubator from 20 to (U flagella-free, round cells, in V. aureus 

 from 1 to 15, are produced in the xegetative half of the mother- 

 colony (Fig. 211). Microgametocytes are variable in number at 

 the generative pole; in V. globator the number is small (from 1 to 5), 

 but in V. aureus, the cells of an entire hemisphere or even more, 

 may become microgametocytes (Fig. 211, B, D). In each micro- 

 gametocyte, plates of microgametes are formed as in Eudorina. 

 They are spindle-shape and somewhat spirally bent with a chromato- 

 phore at the posterior end and a proboscis-like anterior end with 

 laterally inserted ffagella. 



Volvox globator is represented by both vegetative and germinal 

 colonies. The former give rise only to parthenogenetic or asexual 

 daughter colonies, the latter are monoecious producing both macro- 

 and microgametocytes. According to some observers the colonies 

 are protandrous making self-fertilization impossible, but others 

 find that self-fertilization is not infrequent (Klein, Overton, et al.). 

 In Volvox aureus there are pure ^•egetative, pure female and pure 

 male colonies but the progeny of a colony of any type does not of 

 necessity follow the parental type. 



A similar complete differentiation, or oogamy, is shown by the 

 majority of Coccidiomorpha amongst the Sporozoa. In some 

 cases, however, notably in the genus Adelea, gamete differentiation 

 is of the same general t^^De as in the Vorticellidse. In other cases 

 a multitude of minute sperm-like gametes are formed from the 

 mierogametocyte while the macrogamete appears like a slightly 

 modified vegetative individual (Fig. 183, p. 427). In Cyclospora 

 karyolytica, Schaudinn (1605) maintained that differences shown 



