MONOCYSTIS. 13 



. Encystation may occur after conjugation, and apparently 

 as the result of it. The disc becomes retracted ; 

 the cell-body usually separates from its stalk, be- 

 comes spherical, and secretes a cyst around itself. 



D. Action of Reagents. 



Kill some Vorticellce with methyl-green containing a trace 

 of acetic acid ; wash after three minutes with water, 

 and mount in glycerin or balsam. 



f The macro-nucleus will be stained and its shape 

 and relations can be well studied. 



V. MONOCYSTIS. T 



Monocystis belongs to a special class of Protozoa, the 

 Sporozoa or Gregarines. The distinctive characters of this 

 class are their exclusively parasitic nature, absence of a 

 digestive tract, and the formation of resistent spores provided 

 with a thick coat. Monocystis is a common parasite of the 

 earthworm. It occurs in the vesiculse seminales and also in 

 the hinder region of the ccelom, where its spores form masses 

 visible to the naked eye. The attacks of such large numbers 

 of parasites weaken the reproductive system of the worm, 

 and in consequence reduce both the size and fertility of 

 the seminal vesicles. At least three species of Monocystis 

 are known. 



Make a cover-glass preparation of the contents of a vesicula 

 seminalis taken from an infected worm, according to the 

 method described on p. 82. Search the preparation for the 

 free and encysted Monocystis. 



The stage in the life-history of Monocystis before spore- 

 formation is the nutritive phase, and hence the term ' tro- 

 phozoite ' may then be applied to the animal. To the later 

 stage the term ' gametocyte ' is applicable. 



A. Structure. 



Each trophozoite is a single cell with a single nucleus. 



