550 
ZOOLOGY: KOFOID AND CHRISTIANSEN 
spinning out a temporary paradesmose between them upon the outside 
of the persistent nuclear membrane. The nucleus, from which an intra- 
nuclear chromidial cloud had emerged, with subsequent increase of 
cytoplasmic chromidia, exhibits an enlargement of the karyosome, its 
breaking up into eight chromatic granules probably representing four 
precociously split chromosomes which form in parallel rows and merge 
into a split skein from which four chromosomes emerge in the equatorial 
plate at the metaphase. These constrict, the daughter chromosomes 
migrate toward the poles of the intranuclear spindle, and the nuclear 
membrane constricts the parent into two daughter nuclei. 
Plasmotomy is long delayed. The separation is longitudinal, the two 
daughter nuclei of each side forming the nuclei of the daughter zooids, 
which hang together assuming a great variety of positions before the 
protoplasmic bridge finally parts. 
Multiple fission is of three types. The first is in free individuals in 
which three mitoses follow in succession before plasmotomy occurs 
and each zooid during the process acquires its full complement of organ- 
elles before the next division ensues. The result is a 16-nucleate, free- 
moving Plasmodium composed of 8 fully equipped zooids which they 
separate singly. These small individuals are not Octomitus-]ike and are 
not to be confused with Hexamitus muris Grassi ( = Octomitus) , which 
species occurs in the same host with G. muris. Giardia, according to 
our evidence, does not pass through an Octomitus stage as Hartmann 
(1911) proposed. 
Multiple fission in free forms occurs also by nuclear division with 
which the extranuclear organelles do not keep pace in multiplication, 
so that free individuals with the normal single equipment of these of 
extranuclear organelles are crowded with 16 nuclei in a bilateral or ulti- 
mately an irregular arrangement. The later history of such individuals 
has not been traced. 
Single encysted individuals may also undergo multiple fission. The 
extranuclear organelles tend to disappear, the axostyle and posterior 
peristome lingering longer than the other chromatic parts as the nuclei 
go through three succeeding divisions producing a 16-nucleate mass 
within the cyst. Such cysts seem not to undergo further development 
in the rectum of the host in which they are found. 
We find no evidence that the so-called conjugation cysts contain two 
sister individuals, and that therefore autogamy occurs. Pairs of indi- 
viduals in end-to-end back-to-back position as in cysts are found free 
without evidence of their origin by fission. This condition may pre- 
cede encystment. The two individuals which may simulate maturation 
