ZOOLOGY: KOFOID AND CHRISTIANSEN 
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gins. The flagella form a part of an integrated neuromotor system of 
fibrils which unite the two component cells by a single chromatic system 
staining more or less deeply with iron haematoxylin. This system con- 
sists of a rhizoplast from the centrally located karyosome of each nu- 
cleus which passes through the centrosome on the nuclear membrane 
to the blepharoplast on its side at the head of the axostyle. 
From the two blepharoplasts the single axostyle (not two as hereto- 
fore reported) passes posteriorly to emerge as the posterior pair of 
flagella. From the blepharoplast or near it, also arise the other fla- 
gella. The antero-lateral passes forward within the cytoplasm, crosses 
its mate of the opposite side uniting at the crossing in a node, the an- 
terior chiasma, and thence curves posteriorly along the margin of the 
cytostome to emerge from the lateral basal granule as a free antero- 
lateral flagellum . The postero-lateral passes obHquely posteriorly within 
the cytoplasm to emerge near the margin, and the free ventrals emerge 
at once on the ventral surface. The blepharoplasts of the two sides 
of the axostyle are united across its head by a transverse bridge com- 
missure. The antero-lateral flagella run in close conjunction with the 
thickened chromatic anterior peristome and the postero-laterals are in 
contact with the posterior arc of the peristome. This thickened chro- 
matic margin lies in the rim of the deeply cupped ventral cytostome, the 
organ of attachment of the parasite. 
Dorsal to the axostyle is a pair of chromatic bodies, the parabasals 
which contain stainable material whose volume fluctuates with the con- 
ditions of metabolism and which may function as reservoirs of cyto- 
plasmic chromidial material. They appear to have a characteristic 
shape in each species. In G. muris they are stout ellipsoidal, and 
nearly fused. In G. microti (fig. 1) they are slender, curved, tapering, 
parallel structures. In G. muris each is connected with the axostyle near 
the blepharoplast by a slender chromatic fibre. 
These organisms multiply in both the free and the encysted stages, 
by simple binary fission, and by multiple fission leading to the forma- 
tion of a 16-nucleate, 8-zooid plasmodium or somatella, or a 16-nucleate, 
potentially 8-zooid cyst. Binary fission occurs by a well defined mitosis 
followed by a delayed plasmotomy. 
Mitosis in Giardia is much like that described by Kofoid and Swezy 
(1915) for Trichomonas. It begins in the blepharoplast whose division 
is followed by that of the axostyle which splits distally to form two on 
the anterior ends of which the daughter blepharoplasts are attached. 
The centrosome at the upper pole of the nucleus divides and the daugh- 
ters assume polar positions on the membrane of the elongating nucleus, 
