1924] Kessel: Amoebae of Culture Rats dud Mi-ce 515 



being large, two medium in size, and the fourth so small that it does 

 not stain as darkly as the others. 



The processes, resulting in the formation of the anaphase and telo- 

 phase, are carried out in a manner similar to those already described 

 for C. muris. 



ENDAMOEBA RATTI sp. nov. 



This species of amoeba has been encountered in only 3 of the 288 

 rats examined to date and in none of the mice. As its characteristics 

 warrant its cla^ifieation with the genus Endamoeba, this species has 

 been named Endamoeba ratti sp. nov. Permanent slides, on which 

 are to be found stained specimens of both the cysts and free amoebae, 

 have been available from two of these three rats. 



The Motile Amo^iba 



Early in this investigation, a motile amoeba was observed in a 

 normal saline preparation which presented characteristics entirely 

 different from those exhibited by the other amoebae found in rats 

 and mice. In comparison M'ith amoebae of the genus Councilmania, 

 the general appearance of this amoeba, when rounded, is more 

 opaque ; the structure of the endopla-sni is more vacuolated and granu- 

 lar; and the pseudopodia never present the characteristic hyaline 

 appearance of the pseudopodia formed by amoeba belonging to the 

 genus Councilmania. 



In progressive movement, the pseudopodia formed are always 

 granular and the endoplasm constantly extends to the outermost 

 margin of the pseudopodium (fig. C). The amoeba does not progress 

 by a looping method, as described for Councilmania, but rather flows 

 forward by a streaming movement, rounding up less often than 

 Councilmania. The nucleus is often located in the extreme anterior 

 end of the amoeba during this forward movement. The posterior, 

 conical projection, already described in Councilmania, is more 

 prominent and more constant in this species. The pseudopodia are 

 cliaracteristically blunt and granular. 



When attached, the amoeba occasionally produces a narrow ecto- 

 plasmic margin when the pseudopodium first begins to form. This 

 lasts only for an instant and the endoplasm immediately flows into 

 it before its completion. A completely formed hyaline pseudopodium 

 has never been seen, and the conical pseudopodia, common in Council- 

 mania, are not formed. On the whole, the amoeboid movement of this 



