56 PROTOZOA. 



blood, there is an intermediate host, or that the spores have the 

 power of developing and living outside the body. 



As a general rule they do not inflict serious damage on their 

 hosts; but in some cases they are very injurious, and may cause 

 death. This is sometimes due to the destruction of large tracts of 

 cells or of great numbers of blood corpuscles. Whether in such 

 cases the injury is due to any other cause than merely eating out 

 the cell, such as the production of an injurious substance as the 

 result of their vital activity, is not known. In some endogenous 

 forms, e.g., Myxosporidia, in which the spores cannot escape from 

 the host, extensive tumours may be formed. 



In the classification of the class adopted in this work, the blood -parasites 

 have been united in the order Hcemosporidia, and the Coccidiidea have been 

 separated from the Gregarinida. It is very probable that these three orders, 

 which are more closely allied to each other than to the other two orders, should 

 be united in one group. 



Order 1. GREGARINIDA.* 



Parasitic Protozoa which are embedded during the whole or a part 

 of their lives in the protoplasm of their hosts. They are without 

 mouth or anus, and they usually reproduce by coated spores. Cilia 

 and pseudopodia are absent. 



The Gregarinida live as parasites in the alimentary canal, and 

 in the tissues of most animals. They are not found in Protozoa, 

 Coelenterates, or Vertebrata. In the young state they lie entirely 

 within the protoplasm of a cell of their host, usually an epithelial 

 cell of the intestine ; but as they grow older and increase in size 

 they project from the cell, to which they remain attached for a 

 time. Eventually they become free, and lie in the cavity of the 

 intestine or other organ of their host. The body is generally 

 elongated in a vermiform manner, and consists of a granular semi- 

 fluid endoplasm containing a nucleus, a thin external layer of clear 

 ectoplasm, and a thick external cuticle. Hooks for attachment, 

 and hair-like processes may be present as modifications of the 

 cuticle. The structure of the body may be complicated by the 

 presence of a partition wall dividing the endoplasm into an anterior 

 portion called the protomerite, and a posterior the deutomerite. 

 The partition consists of a prolongation of the ectoplasm, and the 



* Aime Schneider, " Contributions a 1'histoire des Gregarines des Invertebres 

 de Paris et de Roscoff." Arch, de Zool. exper. et gen., torn, iv., 1875 ; and in 

 various succeeding volumes of the same Journal. O. Biitschli, " Protozoa," in 

 Bronn's Klassen und Ordnungen d. Thierreichs, 1880-2. 



