LOESCHIA 



305 



Cystic Stage. — A cyst is spherical or slightly oval, 12 to 14 microns in dia- 

 meter, and contains a cytoplasm free from food particles, and may or may not 

 - contain a refractile body, while the nucleus is large and contains much 

 chromatin. This nucleus divides, by simple division, forming two daughter 

 nuclei, and this binucleate stage, which is of long duration, is characterized 

 by the throwing out of chromatin from the nuclei. 



Autogamy. — Each nucleus now gives off reduction bodies which are dis- 

 solved in the cytoplasm. These two nuclei are slightly different: in one it is 

 evenly distributed, while in the other it is concentrated at one end ; the former 

 migrates towards the latter, and both become alike and throw out chromatin. 

 The nuclei were not seen to fuse, but they elongate greatly, spindles are 

 formed, and they divide, giving rise to four nuclei — i.e., two pairs at opposite 

 poles of the cysts, composed of one nucleus from each of the original forms 

 extending to the opposite pole of the cysts. 



Fig. 49. — Diagram of the Life-Cycles of L. muris Grassi (con- 

 structed FROM Wenyon's Drawings). 



Each pair then fused to form one nucleus, and then almost immediately 

 divided to form four nuclei, and these again to form eight nuclei. 



During this process the soft gelatinous cyst wall of the precystic stage is 

 converted in a tough resistant envelope, inside which an inner membrane 

 is formed (compare Amceha proteus). The outer cyst wall becomes tough and 

 irregular in the fceces. 



Method of Infection. — The cysts now escape from the intestine in the normal 

 faeces, in which the amoebae are not seen, these being only found in diarrhceal 

 motions. Cysts were used to infect by feeding a mouse, which was apparently 

 free from infection, and in about three to four weeks cysts appeared for the 

 first time in the faeces, 



20 



