218 



PROTOZOA. 



and serve to fix the capsule, while the amoeboid germ creeps out 

 and penetrates the tissues of the host. Experiment shows that 

 fishes are infected through the alimentary canal. 



The Myxosporida frequently cause serious epidemics in fish. This was 

 noticeably the case with the fish in the aquaria at the Chicago exposition. 

 Myxobolus, Myxidium. Invertebrates may also be infected, the celebrated 

 pe*brine of the silkworm being caused by Nosema (Glugea) bombycis. 



Order V. Sarcosporida. 



The Sarcosporida (fig. 159) also called 

 Rainey's or Miescher's corpuscles occur in 

 the voluntary muscles of vertebrates, especially 

 mammals. They are oval cysts lying in sar- 

 colemma sacs between the fibrillse. They have 

 a cyst, the wall of which is radially striped, 

 and inside this, in the ripe condition, are 

 spores, imbedded in a stroma, each spore con- 

 taining numerous renif orm or falciform sporo- 

 zoites. Sarcocystis miescheriana in muscles of 

 pig; S. muris in the mouse; 8. lindemanni 

 rare in human muscle. 



Summary of Important Facts. 



1. The Protozoa are unicellular organisms 

 without true organs or true tissues. 



2. All vital processes are accomplished by 

 the protoplasm (sarcode), digestion directly 

 by its substance, locomotion and the taking 



of food by means of protoplasmic processes (pseudopodia) or by 

 ;appendages (cilia and flagella). 



3. Excretion takes place by special accumulations of fluid, the 

 contractile vacuoles. 



4. Reproduction is by budding or by fission. Conjugation has 

 been witnessed in many, and possibly occurs in all. True con- 

 jugation is a process of fertilization (caryogamy), in contrast to 

 fusion of plasma (plasmogamy). 



5. Protozoa are aquatic, a few living in moist earth; they can 

 only exist in dry air in the encysted condition, surrounded by a 

 capsule which prevents desiccation. 



6. Since encysted Protozoa are easily carried by the wind, the 

 occurrence of these animals in water which originally contained 

 none is easily explained. 



7. The mode of locomotion serves as the basis for division of 



FlO. 159. Sarcocystis 

 miescheriana^ from 

 diaphragm of pig. 

 (After Biitschli.) 6s, 

 cyst; sp, spheres of 

 spores. 



