ZOOLOGY: KOFOID AND CHRISTIANSEN 
551 
divisions in so far that the first division of each nucleus gives rise to two 
nuclei, one with abundant chromatin, and one (first polar nucleus?) 
with little chromatin. The second division occurs in both of these 
daughter nuclei. The smaller nucleus divides forming two still smaller 
nuclei and the larger one forms one nucleus rich in chromatin (the 
gamete nucleus?) and one with little chromatin (the second polar nu- 
cleus?) . However, no evidence of reduction in number of chromosomes 
is demonstrable. It is obvious that, since these divisions occurred in 
both nuclei of the somatella, we might have a binucleate gamete, and 
should the two ^conjugants' in the cyst unite, a binucleate zygote, a 
condition highly improbable. The alternative explanation of this simu- 
lation of maturation is that we have here some form of degenerative 
multiple fission but the evidence of this is not conclusive. 
We find evidence of groups of structural characteristics which are 
diagnostic of the several species in the genus. The same organelles 
with the same fundamental relations of position occur in all of the 
species at comparable stages. The specific differences consist in modifi- 
cations in shape, size, proportions, relative size and shape of the cyto- 
stome and its relation to the margin of the body, in the size, shape, and 
position of the parabasal bodies, in general stainability, and in relations 
to hosts. It is possible thus to characterize G. agilis Alexeieff from the 
tadpole, G. sanguinis (Gonder) from Elanus, sl South African falcon, 
G. duodenalis (Davaine) from the European rabbit, G. muris (Grassi), 
from Mus, Epimys, Arvicola (?) and Peromyscus, G. microti, sp. nov. 
from Microtus, and the species widely known as Lamhlia intestinalis 
(Lamxbl) from man. Conclusions as to the identity of Giardia 
( = Lamhlia) of man and rodents now generally accepted are of 
doubtful validity and require critical verification. 
The generic name Lamhlia Blanchard 1888 should give way to Giardia 
Kunstler 1882 on ground of priority since species of the two are mor- 
phologically so alike that no generic distinction can be made between 
them. 
Our work has shown that Giardia muris and G. microti produce a 
readily recognizable enteritis in mice, and that both binary and multi- 
ple fission take place in the free non-encysted stage. It may be found 
abundantly in material well smeared out from the intestinal epithelium. 
Multiple fission results in a 16-nucleate, 8-zooid plasmodium which 
later undergoes disintegrative plasmotomy. There is no Octomitus 
stage in the life-history of Giardia. There is typically one axostyle in 
the trophozoite. Prophase stages in which this has divided to form 
two axostyles are often seen. The so-called ^Ratzelkorper' are homo- 
