116 University of California Publications in Zoology ["Vol. 19 



of Giardia found in culture rats. This species of Giardia resembles 

 G. microti as far as the general form of the body and the organelles 

 are concerned. The species is longer than G. microti, measuring 13 

 to 17 microns in length and 6 to 9 microns in width. The cysts, 

 however, are approximately the same size as those of G. microti; they 

 measure 11 to 13 microns in length and 5 to 7 microns in width 

 (compare pi. 1, figs. 5, 13). 



The locus of infection in the rat differs from that of the meadow 

 mouse. In the meadow mouse the flagellates were found in all the 

 regions of the small intestine, but in the rat the jejunum is the area 

 that is most heavily infected. No flagellates occurred in the duodenum 

 and only a few in the ileum. Again, it was found that the intestine 

 of the meadow mouse was not discolored by an infection with Giardia 

 (Boeck, 1917), but in the rat the jejunum is orange colored and filled 

 with gas when Giardia are present. This latter condition is very 

 similar to the condition found in culture mice and Peromyscus gamheli 

 when infected with G. muris. 



A study was made of the cysts found in the different regions of 

 the small and large intestines in order to see if the method of develop- 

 ment for this species of Giardia during encystment was similar to 

 that of G. microti during its encystment. 



The following table gives the types of cysts found in the different 

 regions of the digestive tract of the mouse. 



It will be seen at once that the only types of cysts encountered 

 in the preparations were the single-individual and the binary cysts; 

 no multinucleate cysts were ever found. In the meadow mouse the 

 binary cysts did not occur until the cysts had reached the colon on 

 their transit through the intestine to the outside of the mouse, but in 

 the rat the binar}^ cysts occurred in the jejunum along with the 

 flagellates in the free state. The single-individual cysts were few in 

 number compared with the binary cysts, and so it would seem that the 



