188 SEX IN MICROORGANISMS 



reproduction is commonly by multiple fission (binary fission in 

 Babesia). In the Eugregarinina, increase in numbers does not take 

 place during the trophic period but is provided for by the production 

 of large numbers of gametes by gamonts encysted in pairs, and also 

 by multiplication within the oocyst or spore membranes. 



Order Gregarmida 



In this group, both isogamy and anisogamy have been described, 

 but in anisogamy there is usually not the extreme divergence between 

 the gametes found in the Coccidia and Haemosporidia. However, the 

 male gamete may be relatively slender (Fig. T, 54; Leger and 

 Duboscq, 1903), and it sometimes has a flagellum (Leger and Du- 

 boscq, 1909; Goodrich, 1949). 



The life history of a gregarine begins when a host swallows one 

 or more spores, each typically containing eight minute sporozoites. 

 When released in the host's digestive tract, the sporozoites usually 

 penetrate into the epithelium; there they may come to rest and begin 

 to grow, or continue on into the coelome or into some coelomic 

 organ. If the early stages of development are intracellular, a tropho- 

 zoite soon outgrows its cellular environment and emerges into the 

 digestive tract (or other cavity), retaining an anchorage to the epi- 

 thelium by means of the epimerite or mucron. 



In many of the cephaline gregarines, some, at least, of the tro- 

 phozoites early become detached and join with another one which 

 may or may not remain attached to the host's tissues (Fig. S, 7, 8). 

 In this association in pairs, or syzygy, the anterior end of the satellite 

 (male) is usually attached to the posterior end of the primite (female) 



Sometimes two or more satellites may be attached to one primite, 

 or there may be a chain of individuals attached one behind the other 

 (Fig. S, 4). In many cases (the so-called solitary species) pairing 

 does not take place until just before encystment. In some gregarines 

 attachment is at the anterior end of both members. This may occur in 

 cephaline species, for example Stylorhynchns ohlongatiis (Fig. T, 

 49; Leger, 1904), or in acephalines, for example Kalpidorhynchiis 

 arenicolae (50; Cunningham, 1907). Pairing may also be lateral, 

 either with "heads" together as in Cystobk chiridotae (51; Dogiel, 



