MORPHOLOGY AND TAXONOMY OF THE SPOROZOA 533 



liberate the germs, nor would there be any normal way of eliminat- 

 ing such spores if formed in the blood. It is quite possible, of course, 

 that germs may make their way into the blood by way of the diges- 

 tive tract and this is realized in the Hemoproteidae and in Hemo- 

 gregarina where final stages in the life history chiefly gametocytes 

 (Hemoproteus) alone are blood-dwelling while other stages occur 

 in the intestinal cells or in the endothelial cells of bloodvessels 

 (Hemoproteus, Haplozoon, Karyolysis). In these cases transmis- 

 sion is brought about by other hosts (flies, mites and leeches) while 

 the definitive host becomes infected by the contaminative method 

 (see also p. 361). 



In Plasmodiidae or malaria organisms the digestive tract of the 

 definitive host is not involved in the life history of the parasite. 

 Here the entire vegetative life is in the blood cells of birds or the 

 red blood corpuscles of mammals. Xo cysts of any kind are formed 

 but the blood, with parasites, is taken into the digestive tract of 

 mosquitoes where fertilization occurs and metagamic products are 

 formed. The final metagamic products— sporozoites— are inocu- 

 lated by the mosquito directly into the blood (see page 406). 

 Accompanying this type of life history is the formation from hemo- 

 globin of the characteristic pigment melanin (Plasmodium, Hemo- 

 proteus) which is absent in forms developing elsewhere than in 

 the blood. Here, also, we note the absence of resistant unchang- 

 ing membranes (oocyst, sporocyst) about the zygote which are 

 typical of the majority of Telosporidia. On the contrary, these 

 zygotes produce delicate fertilization membranes which enlarge 

 with growth and development of the zygote which, immediately 

 after fertilization, has the power of independent movement. 



Other variations will appear in the discussion of the different 

 groups of Sporozoa as given in the following classification, in which, 

 following the majority of students of the Protozoa, we divide the 

 group into two classes— Telosporidia and Cnidosporidia. The two 

 groups have little in common besides the mode of life of parasites. 

 The Class Telosporidia includes those forms in which the life of 

 the individual comes to an end with sporulation. The Class Cnido- 

 sporidia includes those forms in which sporulation occurs in internal 

 buds during the vegetative activity of the individual, sporoblasts 

 being carried about by the still active parent cell. 



Class I. TELOSPORIDIA Schaudinn. 



Telosporidia are Sporozoa which, with very few exceptions, are 

 intracellular parasites during some phase of the life cycle. A new 

 host is infected by contamination or by inoculation and the young 

 germ— a sporozoite— enters some cell element, an epithelial cell if 

 the parasite is one of the Ooecidia, a blood element either blood 



