INVERTEBRATA. 



417 



number of gametes, which conjugate within a cyst in pairs 

 with an equal number of other gametes to form the same 

 number of zygotes, which form the same number of spores, 

 each of which divides into eight sporozoites. 



There is another species of Monocystis, usually found in 

 the same worm with M. agilis. It is larger and is called 

 M. magna. It occurs attached by one extremity of the 

 elongated body to the epithelium of the seminal funnel, 

 and only becomes free in the sperm sac just before encyst- 

 ment and conjugation. 



8. Characters of Coccidiidea. These are Sporozoa 

 which are intracellular parasites living in tissue cells of 

 Metazoa, usually in epithelial cells, not in blood cells. 

 They are chiefly found in Arthropoda, Mollusca, and Verte- 

 brata. The species of Coccidium are usually confined to 

 vertebrates, attacking the cells of the kidney, liver, spleen, 

 or testis, but never the ovary. One species attacks the 

 epithelium of the bile- ducts in young rabbits and causes 

 an acute disease which is often fatal. The liver becomes 

 greatly enlarged, the secretion of bile is diminished, the 

 blood becomes thin and watery, and the animal dies in 

 convulsions, or may survive the acute stage of the disease 

 and recover. 



9. Development of Sporozoite into Schizont. The 



species, however, whose life-history has been most com- 

 pletely investigated is not one that lives in a vertebrate 

 host, but one that occurs in the intestinal epithelium of 

 Litholius forficatus, a centipede. The name of this form 

 is Coccidium schubergi, and the name of its investigator is 

 Schaudinn. The youngest stage of this parasite is a free 

 sporozoite which is sickle-shaped and very minute, mea- 

 suring 15 to 20 /A in length and 4 to 6 /A in breadth. (The 

 symbol //, indicates the thousandth part of a millimetre, or 

 001 mm.) It consists of finely granular protoplasm with- 

 out cuticle, and contains a single nucleus. The latter 

 appears in the living organism as simply a clear trans- 

 parent spot. When killed and stained the nucleus is seen 

 to consist of a number of chromatin granules contained in 

 ZOOL, 27 



