500 BIOLOGY OF THE PROTOZOA 



metabolic activities and full growth the macrosphaeric organism 

 breaks down into a multitude of isogametes which have an entirely 

 different organization from that of the agametes. Whereas the 

 latter are pseudopodiospores, the isogametes are flagellispores, each 

 bearing two similar flagella, and copulation occurs by union of two 

 of these similar flagellispores (Fig. 119, A, C). 



Isogamous microgametes are also quite common in Phyto- 

 monadida and in their formation the usual type of binary fission 

 gives place to multiple division whereby from four {e. g., Polytoma 

 uvella) to many {e. g., StcphanosplKFra, Chlamydomonas) isogametes 

 are formed. Also in the Sporozoa, particularly amongst the 

 Gregarinida, isogametes are characteristic but there is no uniformity 

 in the group and a tendency to anisogamy is pronounced. The 

 same genus {e. g., Monncy.siis) comprises some species with isoga- 

 metes, some with anisogametes. A special and interesting case 

 of isogamete formation is illustrated by the schizogregarine Cyphryo- 

 cystis mesnili a parasite of the cockroach (Fig. 180, p. 425). 



Anisogametes illustrate not only the cyclical differentiation 

 resulting in a different type of reproduction from that of the usual 

 vegetative type but they also illustrate the two divergent effects 

 which such differentiations may bring about, one leading to rela- 

 tively greater stability, storage of metabolic products and relative 

 inactivity, the other leading to a more kinetic organization with 

 freedom from metabolic products. As one would expect there is 

 every gradation in the relative differentiation of anisogametes 

 from forms which might well be regarded as hologametes to the 

 completely differentiated egg-like cells and spermatozoa of the 

 Coccidiomorpha or Volvocidte. 



According to Schaudinn's interpretation of the fertilization pro- 

 cesses in Actinophrys sol (1896) there is a permanent fusion of 

 similar adult cells (hologametes). But the recent investigations 

 of Belaf (1922) show that one of the apparent hologametes develops 

 a pseudopodial process which is the first to unite with the other 

 gamete and undergoes its meiotic divisions more quickly than does 

 its mate (Fig. 209). Similar minute differences in microgametes 

 are characteristic of Monocystis rostrata but the differences become 

 more pronounced in PterocejjhaJiis nohilis, SchaudinrJIa henlecp, 

 or Stylorhynchvs longicuUis. In Phytomonadida also, slight differ- 

 ences may be facultative in Polytoma uxella, more pronounced in 

 Chlorogonium euchlorum and extreme in the genus Volvox (Fig. 211, 

 p. 504), In Sarcodina, apart from Actinophrys sol, there are few 

 cases in which the full develo])ment and fusion of anisogametes 

 have been convincingly demonstrated. Schaudinn (1903) described 

 the formation and union of anisogametes in a Centropyxis aculeata 

 but the confirmation of his arcelliform gametes has not yet appeared. 

 Elpatiewsky (1909) described the fusion of anisogametes in Arcella 



