3!124] Kcssi'I: Amotbcr of CuUitir Rats an, I Mice 511 



pleted rather suddenly. The middle nucleus of fi^ire 18, plate 44, 

 represents the polar cap and chromosomes arranged at either end of 

 the nucleus, only traces of the extreme ends of the spindle fibers 

 remaining, and shows a very marked constriction of the nuclear mem- 

 brane in the middle region. This constriction of the nuclear mem- 

 brane is also shown in figure 10, plate 44, but the nuclear contents 

 have already become arranged in an early prophase of the second 

 division. The upper nucleas (pi. 44, fig. 16), shows the final dividing 

 stage of the nucleus into the two daughter nuclei, the nuclear contents 

 representing a typical resting stage while the lower nucleus of the 

 same figure shows the final separation as having occurred and the 

 nuclear membrane fully formed around each daughter nucleus. 



The process of nuclear division in parasitic amoebae differs from 

 that in the meta^oan cell in that the nuclear membrane remains 

 intact throughout the whole process. It is for this reason that the 

 polar caps of the spindle and the intradesmose connecting them must 

 be formed from material within the nucleus. 



The divisions of the nuclei within the same cyst do not always 

 take place concurrently (pi. 44, fig. 15). Here the larger nucleus 

 represents the first division while the two smaller nuclei have already 

 completed the second division. The nuclei in figure 18 exhibit the same 

 phenomenon : the two larger nuclei have resulted from the second 

 division, the middle nucleus is just completing the third division, and 

 the two small nuclei have already completed the third division. 



COUNCILMANIA DECUMANI (Rudovsky, 1921) emend. Kessel 



Cauncilniania decumani has been found in 14 of the 20 mice and 

 in 9 of the 24 rats examined by us. We believe this is the species of 

 amoeba from rats dealt with, for the most part, at least, in the accounts 

 by Brug (1919) and by Rudovsky (1921). Rudovsky (1921) noted 

 a difference between the amoeba of the mouse and the amoeba of the 

 rat. He called the latter Endamoeba muris decumani. On account 

 of the characteristics to be mentioned in the following account, it is 

 necessary to transfer this species from the genus Endamoeba to which 

 it was assigned by Rudovsky to the genus Councilmania (Kofoid and 

 Swezy, 1921). 



