526 BIOLOGY OF THE PROTOZOA 



Nuclei are single in number in Telosporidia and multiple in the 

 majority of Cnidosporidia. In structure they are highly charac- 

 teristic, particularly in Gregarinida. Here there is a great endosome 

 in vegetative stages of the organism which represents a combination 

 of somatic and germinal chromatin. When ready for sporulation 

 the germinal chromatin leaves the endosome as a small bud and 

 forms chromosomes on a relatively small spindle (Fig. 55, p. 101). 

 The residual mass of endosome and the remainder of the nucleus then 

 disintegrate and disappear. The small aggregate of germinal chro- 

 matin together with its division figure thus resembles a micronucleus 

 of the ciliates while the disintegrating portion is equivalent to the 

 macronucleus. 



The chromosomes of Telosporidia give more evidence of indi- 

 viduality than do those of any other group of Protozoa. Meiotic 

 phenomena are of two general types— so-called gametic meiosis in 

 which reduction in number of chromosomes occurs during the 

 formation of gametes, and zygotic meiosis in which reduction 

 occurs during the first mitotic division of the amphinucleus. Both 

 types are found in Eugregarinida (Monocystis, Diplocystis, etc.) 

 and Coccidia (Aggregata). The number of chromosomes in gregar- 

 ines is often uneven (3, 5, 7, etc.) which indicates either zygotic 

 meiosis (Dobell, Jameson) or zygotic synapsis (Naville, see p. 309). 



Asexual reproduction may occur by equal division (e. g., Ophryo- 

 cystis, Babesia, etc.), by budding which may be exogenous (Myxo- 

 sporidia) or endogenous (as in the gregarines Schizocystis and 

 Eleutheroschizon) , or by multiple division (Coccidiomorpha). Re- 

 production following fertilization always involves the formation 

 and the permanent fusion of gametes. These may be isogamous or 

 anisogamous and dimorphic gametes as different as are eggs and 

 spermatozoa of the Metazoa are characteristic of the Coccidia and 

 Hemosporidia. Sexual processes of peculiar type and regarded as 

 self fertilization or autogamy are characteristic of the Cnidosporidia 

 where such processes with resulting sporulation take place in endo- 

 genous buds. 



Sporulation following fertilization in the majority of forms 

 involves adaptations for preservation of the species during exposure 

 to the conditions external to the definitive host. Such spores are 

 protected against drought and other external conditions by resistant 

 spore membranes or capsules which are opened or dissolved only in 

 the digestive tract of a new host. In the majority of cases such new 

 hosts are individuals of the same species and infection is brought 

 about by eating contaminated food. In many forms, however, the 

 life cycle involves a change of hosts, the metagamic spores develop- 

 ing in one type of animal and the sexual phases of the parasite 

 developing in another type belonging to an entirely different group 

 of the animal kingdom. Thus vegetative stages of the genus Aggre- 



