18 



Balantidium entozoon — This species is commonly found in the 

 rectum of frogs and will be studied in the practicum. Possesses four 

 contractile vacuoles. 



Various other species of Balantidium also infest frogs and certain 

 ones have been found in the body cavity of annelid worms. 



Nyctotherus cordiformis is a form found in the large intestine 

 of the frog and sometimes mistaken for Balantidium entozoon. Differs 

 in being larger, having one contractile vacuole, more prominent 

 persistome, and less strongly curved nucleus. 



Opalina ranarum — Rectum of frog. 



Form and structure — Large enough to be seen as minute, whitish, 

 actively moving spots, 600-800/^ in size. Body flat, disk-like, or 

 oval; divided into ectosarc and endosarc. Cilia uniform in size. 

 Multinucleate. Mouth, gullet, and contractile vacuole lacking, 

 food being directly absorbed. 



Reproduction — Ordinary cross or oblique division. Also, repeated 

 binary fission, the minute forms so produced encysting and passing 

 out with feces of the frog, at the breeding season. Taken up by 

 tadpoles, cyst dissolves, liberating a lanceolate, uninucleate form, 

 which develops into the adult, multinucleate Opalina. 



Sub Phylum SPOROZOA 



Order Gregarinida 



Coelom-inhabiting sporozoa, reproducing usually by spore- 

 formation alone, and after the fertilizing union of but slightly dif- 

 ferent gametes. Following Lankester, '03, take as a type: 



Monocystis agilis — Found in the seminal vesicles of the common 

 earthworm. The majority of individuals of this worm are infested. 



Trophozoite, earliest known stage, minute, nucleated, amoeboid. 

 Lives in one of the sperm morulse floating in the sperm sac, and grows 

 at the expense of the developing sperm cells. Ectosarc and endosarc 

 present. Motility due to longitudinal myonemes. Adult tro- 

 phozoite known as 



Gametocyte, which is ready for reproduction. Two gametocytes 

 associate and form a cyst, but do not fuse. Independently within 

 each gametocyte there is a formation of a segmentation nucleus 

 which divides repeatedly and with their surrounding protoplasm 

 constitute the gametes. These fuse in pairs to form 



