OF THE ALIAIENTARY TRACT 221 



in multiples of the female, thus continuing the anal- 

 ogy with germ cells of multicellular animals, meets 

 the passive, large, ovum-like Macrogamete, it pene- 

 trates at one pole, the nuclei of the two unite, and 

 the thus fertilized cell becomes the so-called Zygote 

 (15), which is then an inert body in the lumen of 

 the intestine. 



Since this is the phase which is destined to con- 

 tinue the species in a new host and must withstand 

 external exposure in the process of transfer, it must 

 be resistant. It therefore becomes encysted, secret- 

 ing a cyst wall, and is now called an Oocyst. It is 

 this cyst in some stage of development which is ob- 

 served in the evacuated intestinal contents and upon 

 which the diagnosis of the infection depends. 



As the Oocyst develops, passing down the intestine 

 and even after passage in the stool, the protoplasm 

 contracts and the nucleus divides and multiplies to 

 a number characteristic of the species ( 16) . Division 

 of cytoplasm now occurs around the nuclei, to form 

 an equal number of rounded bodies, called the Sporo- 

 blasts (17), leaving a remnant of the old protoplasm 

 as unused residue. Each Sporoblast now secretes 

 its own cyst wall, becoming encysted within the 

 Oocyst, the subcyst called the Sporocyst and each 

 enclosed body now a Spore (18). The organism in 

 each Spore divides into an equal and characteristic 

 number of worm-like bodies, being called Sporo- 

 zoites. This process of formation of spores in the 

 Oocyst is called Sporogony. The ripe Oocyst (18) is 



