60 



What is (a) Exogenous, (b) Endogenous Generation ? 



When the life-cycle is adapted for spreading the species 

 to new hosts, the generation is termed exogenous (cross- 

 infective). 



When it is adapted for further multiplication within 

 one host, the generation is called endogenous (self -infective). 

 In many Sporozoa both generations occur. In Monocystis 

 there is only exogenous generation. 



Explain the Terms Sporogony and Schizogony. 



Many Protozoa (especially Sporozoa) reproduce by a 

 process of multiple fission, and the result is a numerous 

 brood of spores. When this multiple fission is preceded 

 by conjugation of gametes with subsequent formation 

 of spores (the sporozoites), usually with resistent coats, 

 for dissemination outside the host, the process is called 

 Sporogony ; and it is characteristic of exogenous generation. 



When the multiple fission is not preceded by conjugation 

 of gametes, and the result is formation of spores (the mero- 

 zoites), which are naked, for further multiplication within 

 the host, the process is called Schizogony ; and it is char- 

 acteristic of endogenous generation. 



In Monocystis sporogony is the only process. 



In which ways (in Sporozoa) may the Infection of a New 

 Host be brought about ? 



In most instances (e.g., Monocystis) the mode of infection 

 is direct and casual ; the spores or germs are taken up 

 accidently by the new host. In certain instances (especi- 

 ally Sporozoa parasites of the blood) it is indirect and 

 inoculative, through an intermediate host ; e.g., the malaria 

 germs are taken up by a mosquito, a blood-sucking insect 

 which, when it " bites," transmits the germs. There is 

 a third but exceptional way, by hereditary infection. It 

 is known to occur in Olugea (syn. Nosema), the parasite 

 which causes the destructive " pebrine " in silkworms. 

 The parasites enter the eggs and give rise to spores which 

 infect the succeeding generation. 



