502 University of California Publications in Zoology [Vol. 2U 



eosin stain the nuclei take the iodine stain first and for a brief period it 

 is possible to definitely distinguish the structure; but as the amoeba 

 gradually assumes the red color of the eosin and disintegrates, the 

 well-defined nuclear structure disappears. In the slides stained with 

 iron-haematoxylin, the same distinguishing characteristics are shown 

 that are found in the nuclei of encysted stages. The nuclear mem- 

 brane is very thin and stains very faintly (pi. 43, fig. 3). A vacuole 

 surrounding the nucleus has been figured by Wenyon (1907, pi. 10, 

 fig. 3). This condition has been seen in my own investigations, but I 

 have considered it to be an abnormality resulting from staining rather 

 than as a normal occurrence. 



Little or no chromatin is encrusted on the nuclear membrane (pi. 

 43, figs. 1 and 3 ) . This condition, in which small chromatin granules 

 are found lining the internal margin of the nuclear membrane, is 

 characteristic of a very early prophase. The bulk of the chromatin 

 material within the nucleus occurs in a 'central' karyosome of the 

 dispersed type, in the form of clustered spherical granules which 

 ahvays present a more or less dispersed appearan-ce. At times the 

 granules may be congregated in a dispersed central ma.ss (pi. 43, 

 fig. 4). This dispersed type of karyosome is figured by Wenyon (his 

 pi. 10, figs. 1-3) and while he notes a distinct nucleoliLS (his pi. 10, 

 fig. 1) this is shown as being more dispersed than is the case in 

 C. decumani. A network of faint linin fibers connects the chromatin 

 granules with the nuclear membrane. The average diameter of the 

 nuclei in motile forms is 5.6/i. 



The nuclei do not retain a constant spherical form but are elastic 

 and may be elongated at times. In one instance the nucleus in a living 

 amoeba elongated and constricted so definitely in the middle that it 

 was thought division was in progress. The nucleus, however, soon 

 resumed its normal spherical shape and did not divide. It was kept 

 under careful observation until the amoeba had again assumed a 

 rounded condition. 



Asexual reproduction. — It is assumed that this species of amoeba 

 multiplies by two methods, by binary fission of the motile amoeba and 

 by budding, a modification of multiple fission following encystment. 

 No occurrences of binary fission have been witnessed in the motile 

 stages of this species though motile stages of C decumani have been 

 found in which two nuclei were present (pi. 46, fig. 31) and the la.st 

 stages of a di^'^sion process were seen in a case of C. lafleuri which had 

 been recovered from a case of infection established in a rat (see 

 Kofoid, Swezy, and Kessel, 1923&). 



