3^22 PARASITES OF THE DOINIESTIC ANIMALS 



In the parthenogenetic phase, which occurs in the human host, the 

 female gametocyte sporulates without fertiHzation. After months of 

 latency these spores may pass into the blood current and enter the 

 corpuscles, bringing about a recurrence of malaria after its apparent 

 cure. 



It should be noted in the sexual cycle that the formation of the spo- 

 roblasts is similar to the formation of corresponding reproductive cen- 

 ters of the Coccidia, which pass a portion of their cj^cle external to a host 

 and which are elsewhere referred to (p. 337). The sporoblasts of the Plas- 

 modia, however, differ from those of the Coccidia in having no protect- 

 ing membrane or capusle, in the absence of which protection, the spo- 

 rozoites are unfitted for existence outside the body of a host animal. 



Classification. — Accorchng to their mode of life, Calkins divides the 

 parasitic Protozoa into the following groups. The arrangement is not 

 a natural one and is merely for descriptive purposes: 



1. Enterozoic. — Living in the lumen of the digestive tract. 



2. Coelozoic- — Living in the coelomic cavities of the body. 



3. Cytozoic. — Living throughout the vegetative period as intracel- 

 lular parasites. 



4. Caryozoic. — Passing into the cell to find lodgment in the cell nu- 

 cleus. 



5. Hematozoic. — Living in the blood plasma. 



In some cases the parasite may pass through a number of these modes 

 of life. Thus the plasmodia of malaria are hematozoic in the blood 

 current, cytozoic in the blood corpuscles, enterozoic in the digestive 

 tract of the mosquito, and coelozoic w^hen they pass as sporozoites into 

 the body cavit.v of this insect. 



In the arrangement of the classification of the Protozoa which follows, 

 only those groups containing species of parasitic importance are given. 



Classification of Paeasites of the Phylum Protozoa 



Phylum IV. Protozoa. P. 311. 

 Class A. Phizopoda. P. 324. 

 Order 1. Lobosa. P. 324. 

 Genus and Species: 



Ameba meleagridis. Host, turkey. P. 325. 

 Entameba histolytica. Host, man. P. 326. 

 E. coli. Host, man. P. 326. 

 Class B. Flagellata. P. 326. 

 Order 1. Spirochetida. P. 327. 

 Genus and Species: 



Spirocheta gallinarum. Host, fowl. P. 327. 

 Order 2. Trypanosomatida. P. 328. 



