VITALITY 277 



which easily distinguish them from agametes or vegetative indi- 

 viduals. In many cases the physiological differences at maturity 

 are expressed by a change in the type of division whereby binary 

 fission is replaced by multiple division. Many daughter cells are 

 thus formed from one gametocyte and the term microgametes has 

 been applied to such a brood. The copulating gametes, however, 

 show no distinguishing morphological characteristics and the dif- 

 ferences between them if there are any must be of a chemical or 

 physical nature. In Foraminifera such isogametes are the rule and 

 their formation indicates a well-defined cyclical differentiation of 

 the parental protoplasm. Thus in Polystomellina crispa according to 

 Schaudinn (1903) and Lister (1905) ; in Peneroplis pertusus according 

 to Winter (1907) ; in Trichosphaerium sieboldi according to Schaudinn 

 (1899) and in Foraminifera generally, the young protoplasm after 

 fertilization forms one type of organism termed the microspheric 

 generation which after nuclear fragmentation and chromidia forma- 

 tion reproduces by agamete formation (Fig. 123, p. 235). Such 

 agametes develop without fertilization into organisms of a different 

 type, the difference being shown by the larger size of the initial 

 shell chamber, hence a macrospheric generation. After metabolic 

 activities and full growth the macrospheric 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. 123, A, C). 



According to Schaudinn's interpretation of the fertilization proc- 

 esses 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. 142). Similar minute differences in microgametes 

 are characteristic of Monocystis rostrata but the differences become 

 more pronounced in Pterocephalus nobilis, Schaudinella henleae, or 

 Stylorhynchus longicollis. In Sarcodina, apart from Actinophrys sol, 

 there are few cases in which the full development and fusion of 

 anisogametes have been convincingly demonstrated. Schaudinn 

 (1903) described the formation and union of anisogametes in Cen- 

 tropy.xis aculeata but the confirmation of his arcelliform gametes 

 has not yet appeared. Elpatiewsky (1909) described the fusion of 

 anisogametes in Arcella vulgaris as a part of a very complex life 

 cycle. In both of these testate rhizopods the nuclei of the gametes 

 are derived from chromidia formed in the gametocytes while the 

 cell bodies are formed by multiple division of the protoplasm. In 

 Radiolaria, according to Brandt (1885) and Borgert (1900), the 



